Error- "Unable to start iproxy. Is it installed?"

When We run our code on one machine it works fine however on another machine it fails with the below error:
We are using the same steps to sign the WDA on the device, working on the same appium server etc…
Any idea why it fails?

The error:
[XCUITest] Error: Unable to launch WebDriverAgent because of xcodebuild failure: “Unable to start iproxy. Is it installed?”. Make sure you follow the tutorial at https://github.com/appium/appium-xcuitest-driver/blob/master/docs/real-device-config.md. Try to remove the WebDriverAgentRunner application from the device if it is installed and reboot the device.

The log:
[debug] [MJSONWP] Calling AppiumDriver.createSession() with args: [{“app”:"/Users/meny.peled/git/iOS_V6_Appium/Beta_Running.app",“clearSystemFiles”:“true”,“newCommandTimeout”:45,“platformVersion”:“11.0.3”,“xcodeOrgId”:“7Y5J2RJXYV”,“automationName”:“XCuiTest”,“useNewWDA”:“false”,“udid”:“51d8c712258a5b0ac63516aa5be9d10014b0c270”,“platformName”:“iOS”,“deviceName”:“iPhone 5S (Meny)”,“xcodeSigningId”:“iPhone Developer”},null,null]
[debug] [BaseDriver] Event ‘newSessionRequested’ logged at 1510514144346 (21:15:44 GMT+0200 (IST))
[Appium] Creating new XCUITestDriver (v2.51.1) session
[Appium] Capabilities:
[Appium] app: ‘/Users/meny.peled/git/iOS_V6_Appium/Beta_Running.app’
[Appium] clearSystemFiles: ‘true’
[Appium] newCommandTimeout: 45
[Appium] platformVersion: ‘11.0.3’
[Appium] xcodeOrgId: ‘7Y5J2RJXYV’
[Appium] automationName: ‘XCuiTest’
[Appium] useNewWDA: ‘false’
[Appium] udid: ‘51d8c712258a5b0ac63516aa5be9d10014b0c270’
[Appium] platformName: ‘iOS’
[Appium] deviceName: ‘iPhone 5S (Meny)’
[Appium] xcodeSigningId: ‘iPhone Developer’
[BaseDriver] Capability ‘useNewWDA’ changed from string to boolean. This may cause unexpected behavior
[BaseDriver] Capability ‘clearSystemFiles’ changed from string to boolean. This may cause unexpected behavior
[BaseDriver] Session created with session id: 1b0d3826-3c8a-4fc2-aac0-372069b1b87b
[debug] [XCUITest] Xcode version set to ‘9.1’ (tools v9.0.1.0.1.1506734476)
[debug] [XCUITest] iOS SDK Version set to ‘11.1’
[debug] [BaseDriver] Event ‘xcodeDetailsRetrieved’ logged at 1510514144442 (21:15:44 GMT+0200 (IST))
[debug] [XCUITest] Available devices: 51d8c712258a5b0ac63516aa5be9d10014b0c270
[debug] [XCUITest] Creating iDevice object with udid ‘51d8c712258a5b0ac63516aa5be9d10014b0c270’
[XCUITest] Determining device to run tests on: udid: ‘51d8c712258a5b0ac63516aa5be9d10014b0c270’, real device: true
[BaseDriver] Using local app ‘/Users/meny.peled/git/iOS_V6_Appium/Beta_Running.app’
[debug] [BaseDriver] Event ‘appConfigured’ logged at 1510514144563 (21:15:44 GMT+0200 (IST))
[debug] [XCUITest] Checking whether app ‘/Users/meny.peled/git/iOS_V6_Appium/Beta_Running.app’ is actually present on file system
[debug] [XCUITest] App is present
[debug] [iOS] Getting bundle ID from app ‘/Users/meny.peled/git/iOS_V6_Appium/Beta_Running.app’: ‘alpha.skygiraffe.skygiraffe’
[debug] [BaseDriver] Event ‘resetStarted’ logged at 1510514144566 (21:15:44 GMT+0200 (IST))
[debug] [XCUITest] Reset: running ios real device reset flow
[debug] [BaseDriver] Event ‘resetComplete’ logged at 1510514144566 (21:15:44 GMT+0200 (IST))
[debug] [iOSLog] Attempting iOS device log capture via libimobiledevice idevicesyslog
[debug] [iOSLog] Starting iOS device log capture with: ‘idevicesyslog’
[debug] [BaseDriver] Event ‘logCaptureStarted’ logged at 1510514144704 (21:15:44 GMT+0200 (IST))
[XCUITest] Setting up real device
[debug] [XCUITest] Installing ‘/Users/meny.peled/git/iOS_V6_Appium/Beta_Running.app’ on device with UUID ‘51d8c712258a5b0ac63516aa5be9d10014b0c270’…
[debug] [XCUITest] The app has been installed successfully.
[debug] [BaseDriver] Event ‘appInstalled’ logged at 1510514150791 (21:15:50 GMT+0200 (IST))
[XCUITest] Using WDA path: ‘/usr/local/lib/node_modules/appium/node_modules/appium-xcuitest-driver/WebDriverAgent’
[XCUITest] Using WDA agent: ‘/usr/local/lib/node_modules/appium/node_modules/appium-xcuitest-driver/WebDriverAgent/WebDriverAgent.xcodeproj’
[debug] [XCUITest] Capability ‘useNewWDA’ set to false, so trying to reuse currently running WDA instance at ‘http://localhost:8100/
[debug] [JSONWP Proxy] Proxying [GET /status] to [GET http://localhost:8100/status] with no body
[debug] [XCUITest] WDA is not listening at ‘http://localhost:8100/’. Rebuilding…
[debug] [BaseDriver] Event ‘wdaStartAttempted’ logged at 1510514150812 (21:15:50 GMT+0200 (IST))
[XCUITest] Launching WebDriverAgent on the device
[debug] [XCUITest] Carthage found: ‘/usr/local/bin/carthage’
[debug] [XCUITest] Killing running processes ‘xcodebuild.*51d8c712258a5b0ac63516aa5be9d10014b0c270, iproxy 8100’ for the device 51d8c712258a5b0ac63516aa5be9d10014b0c270…
[debug] [XCUITest] ‘pgrep -nif xcodebuild.*51d8c712258a5b0ac63516aa5be9d10014b0c270’ didn’t detect any matching processes. Return code: 1
[debug] [XCUITest] ‘pgrep -nif iproxy 8100’ didn’t detect any matching processes. Return code: 1
[debug] [XCUITest] Starting iproxy to forward traffic from local port 8100 to device port 8100 over USB
[XCUITest] Error starting iproxy: ‘Command ‘iproxy’ not found. Is it installed?’
[debug] [BaseDriver] Event ‘wdaStartFailed’ logged at 1510514151041 (21:15:51 GMT+0200 (IST))
[debug] [XCUITest] Unable to launch WebDriverAgent because of xcodebuild failure: “Unable to start iproxy. Is it installed?”. Make sure you follow the tutorial at https://github.com/appium/appium-xcuitest-driver/blob/master/docs/real-device-config.md. Try to remove the WebDriverAgentRunner application from the device if it is installed and reboot the device.
[debug] [XCUITest] Quitting and uninstalling WebDriverAgent, then retrying
[XCUITest] Shutting down sub-processes
[XCUITest] Shutting down iproxy process (pid undefined)
[debug] [XCUITest] Removing WDA application from device
[XCUITest] Error: Unable to launch WebDriverAgent because of xcodebuild failure: “Unable to start iproxy. Is it installed?”. Make sure you follow the tutorial at https://github.com/appium/appium-xcuitest-driver/blob/master/docs/real-device-config.md. Try to remove the WebDriverAgentRunner application from the device if it is installed and reboot the device.
at XCUITestDriver.quitAndUninstall$ (…/…/lib/driver.js:381:13)
at tryCatch (/usr/local/lib/node_modules/appium/node_modules/babel-runtime/regenerator/runtime.js:67:40)
at GeneratorFunctionPrototype.invoke [as _invoke] (/usr/local/lib/node_modules/appium/node_modules/babel-runtime/regenerator/runtime.js:315:22)
at GeneratorFunctionPrototype.prototype.(anonymous function) [as next] (/usr/local/lib/node_modules/appium/node_modules/babel-runtime/regenerator/runtime.js:100:21)
at GeneratorFunctionPrototype.invoke (/usr/local/lib/node_modules/appium/node_modules/babel-runtime/regenerator/runtime.js:136:37)
at
at process._tickCallback (internal/process/next_tick.js:188:7)
Error: Unable to launch WebDriverAgent because of xcodebuild failure: “Unable to start iproxy. Is it installed?”. Make sure you follow the tutorial at https://github.com/appium/appium-xcuitest-driver/blob/master/docs/real-device-config.md. Try to remove the WebDriverAgentRunner application from the device if it is installed and reboot the device.
at XCUITestDriver.quitAndUninstall$ (…/…/lib/driver.js:381:13)
at tryCatch (/usr/local/lib/node_modules/appium/node_modules/babel-runtime/regenerator/runtime.js:67:40)
at GeneratorFunctionPrototype.invoke [as _invoke] (/usr/local/lib/node_modules/appium/node_modules/babel-runtime/regenerator/runtime.js:315:22)
at GeneratorFunctionPrototype.prototype.(anonymous function) [as next] (/usr/local/lib/node_modules/appium/node_modules/babel-runtime/regenerator/runtime.js:100:21)
at GeneratorFunctionPrototype.invoke (/usr/local/lib/node_modules/appium/node_modules/babel-runtime/regenerator/runtime.js:136:37)
at
at process._tickCallback (internal/process/next_tick.js:188:7)
[debug] [XCUITest] ‘pgrep -nif xcodebuild.*51d8c712258a5b0ac63516aa5be9d10014b0c270’ didn’t detect any matching processes. Return code: 1
[debug] [XCUITest] Cannot find xcodebuild’s process id, so unable to retrieve DerivedData folder path
[XCUITest] No WebDriverAgent derived data available, so unable to clear system files
[debug] [iOSLog] Stopping iOS log capture
[MJSONWP] Encountered internal error running command: Error: Unable to launch WebDriverAgent because of xcodebuild failure: “Unable to start iproxy. Is it installed?”. Make sure you follow the tutorial at https://github.com/appium/appium-xcuitest-driver/blob/master/docs/real-device-config.md. Try to remove the WebDriverAgentRunner application from the device if it is installed and reboot the device.
at XCUITestDriver.quitAndUninstall$ (…/…/lib/driver.js:381:13)
at tryCatch (/usr/local/lib/node_modules/appium/node_modules/babel-runtime/regenerator/runtime.js:67:40)
at GeneratorFunctionPrototype.invoke [as _invoke] (/usr/local/lib/node_modules/appium/node_modules/babel-runtime/regenerator/runtime.js:315:22)
at GeneratorFunctionPrototype.prototype.(anonymous function) [as next] (/usr/local/lib/node_modules/appium/node_modules/babel-runtime/regenerator/runtime.js:100:21)
at GeneratorFunctionPrototype.invoke (/usr/local/lib/node_modules/appium/node_modules/babel-runtime/regenerator/runtime.js:136:37)
at
at process._tickCallback (internal/process/next_tick.js:188:7)
[HTTP] <-- POST /wd/hub/session 500 17373 ms - 480
[HTTP] --> POST /wd/hub/session {“desiredCapabilities”:{“app”:"/Users/meny.peled/git/iOS_V6_Appium/Beta_Running.app",“clearSystemFiles”:“true”,“newCommandTimeout”:45,“platformVersion”:“11.0.3”,“xcodeOrgId”:“7Y5J2RJXYV”,“automationName”:“XCuiTest”,“useNewWDA”:“false”,“udid”:“51d8c712258a5b0ac63516aa5be9d10014b0c270”,“platformName”:“iOS”,“deviceName”:“iPhone 5S (Meny)”,“xcodeSigningId”:“iPhone Developer”}}
[debug] [MJSONWP] Calling AppiumDriver.createSession() with args: [{“app”:"/Users/meny.peled/git/iOS_V6_Appium/Beta_Running.app",“clearSystemFiles”:“true”,“newCommandTimeout”:45,“platformVersion”:“11.0.3”,“xcodeOrgId”:“7Y5J2RJXYV”,“automationName”:“XCuiTest”,“useNewWDA”:“false”,“udid”:“51d8c712258a5b0ac63516aa5be9d10014b0c270”,“platformName”:“iOS”,“deviceName”:“iPhone 5S (Meny)”,“xcodeSigningId”:“iPhone Developer”},null,null]
[debug] [BaseDriver] Event ‘newSessionRequested’ logged at 1510514161785 (21:16:01 GMT+0200 (IST))
[Appium] Creating

The problem was in brew.
once I ran brew doctor it helped me to link it & that fixed the problem.

See the related post that helped me in fixing the issue: