I wasn't able to reproduce this issue with the example project we provide. Is this happening only in your own project?
You could try to see if original files in the Unity project are corrupted somehow, and try to replace them with the ones from the example project if that is the case. The libWikitude2UnityBridge.a is located in Assets/Plugins/iOS and WikitudeUnityPlugin.dll is located in Assets/Wikitude/Dependencies.
These files are required for Wikitude to work correctly.
On further investigation I have now seen this happen for other Plugin files, so it appears this is not a Wikitude related issue.
I have posted to Unity Answers to see if anyone has a solution.
Building for Android works fine.
When I build for ios I get:
UnauthorizedAccessException: Access to the path "/Project/ios/Libraries/Plugins/iOS/libWikitude2UnityBridge.a" is denied.
UnauthorizedAccessException: Access to the path "/Project/ios/Data/Managed/WikitudeUnityPlugin.dll" is denied.
If I navigate to those files in Finder and delete them then build again it works sucessfully.
Next time I build I get those files locked again.
Any ideas how this can be resolved?
I started to look for a prebuild step to remove those files but that seems an unsatisfactory solution.