Unexpected error:Error :Can't set headers after they are sent

appium 1.3.1 , ios 8, C# client.

I am sending a long string(more than 300 characters) to textbox.
After 60 seconds webdriver timeout exception is thrown. Howevr sendkeys operation is continued.

Please tell me how to avoid this error and is there any other method to send a long string except sendkeys

Thanks.