Help with transfer of scripts

I have a project that I work on with a buddy for a couple 2-3 months now and we used Unity Version Control to transfer the data. Everything worked fined until now when on my machine everything is normal, but on his machine every single script says on all gameObjects:

The associated script can not be loaded. Please fix any compile errors and open Prefab Mode and assign a valid script to the Prefab Asset

If he tries to add any script to any object outside or inside the prefab mode it gives the error:

Canā€™t add script component ā€˜(name_of_script)ā€™ because the script class cannot be found. Make sure that there are no compile errors and that the file name and class name match.

Why does this happened and why on my PC works, but on his does not?