Error message: Google.IOSResolver.dll' will not be loaded due to errors: Unable to resolve reference UnityEditor.iOS.Extensions.Xcode

I am getting this error message and i was wandering how to fix the problem or even what the problem is, please someone help:

Assembly ‘Assets/ExternalDependencyManager/Editor/1.2.177/Google.IOSResolver.dll’ will not be loaded due to errors:
Unable to resolve reference ‘UnityEditor.iOS.Extensions.Xcode’. Is the assembly missing or incompatible with the current platform?
Reference validation can be disabled in the Plugin Inspector.