The error message 'Unity unable to find player assembly' typically occurs because Unity cannot locate a specific assembly (DLL) that is referenced in your project. This can occur for various reasons:
Incorrect Path: The assembly file is not located in the path specified in your project settings or code.
Missing Assembly: The assembly file might be missing from your project entirely. This can happen if the file has been mistakenly deleted, moved, or was not included when the project was initially set up.
Invalid References: References within the assembly itself might be incorrect, outdated, or pointing to non-existent locations. This often happens after updating or changing dependencies in your project.
Incompatible Assembly Version: If the version of the assembly does not match the one expected by Unity, it might not be recognized correctly.
To resolve this issue, follow these steps:
Check the Path: Make sure the assembly file is in the correct location as per your project files or settings. Unity usually looks for assemblies under the 'Assets' directory.
Verify the Assembly: Check if the assembly file exists in your project at all. If it doesn't, you'll need to add it back into your project. Ensure it is the correct version and is compatible with your current setup.
Update References: If the assembly is present but still not found, check the references within the assembly. Update any outdated or incorrect references. In some cases, you may need to open the DLL in an external tool to do this.
Reinstall/Update Dependencies: If the problem persists, it might be due to outdated or incompatible dependencies. Try updating them or reinstalling if necessary.
Clean and Rebuild: As a final step, try cleaning and rebuilding your project. This can fix issues that arise from cached data.
Remember to back up your project regularly to prevent the loss of important files and settings.