See
Basically, in theory, these should be the steps which should work:
- Rename all files which have the name of the project as part of the file name.
- Do find&replace inside all files, replacing the old project name with the new one.
The problem you have is because the symbol library cache is referenced inside the schematic file and you renamed the cache file. EDIT: you didn’t copy it all. It’s needed for the symbols in the .sch file to work, and it’s referenced by name in the .sch file.