Hey there @ThorkellFr! Welcome to the community! Does this error occur with all projects or just this one? This is reminiscent of an error with a reserved name that was causing issues with unrelated files, resolved here, but doesn’t seem to be exactly it. I’d still recommend reading over that thread just in case.
The error is mentioning a resource being unavailable, which would mean my first recommendation (which you had already tried) is to verify the engine’s files and even double check the location listed to make sure that file is in fact not missing. After that, running the engine as administrator and double checking permissions to hopefully clear some file location permission issues if that’s the case.