As UIAutomation was deleted from xcode 8 (now it uses XCUI technology) and you are trying to run inspector using UIAutomation it creates exceptions like yours. You need to decide if you are still using 7.3.1 xcode with appium 1.5.3 or upgrade appium to 1.6. But appium does not provide inspector for XCUI yet. It is only server 1.6
There are workarounds suggested here https://medium.com/@chenchaoyi/the-options-of-inspecting-ios-10-app-with-appium-1-6-534ba166b958#.cw7fuu5ob
As for me I have not tried if it works. But you can try your luck.
Good luck!