Sessions problems on CI4

Hi, I have on my localhost with xampp on windows 11 several ci4 installations.
They worked fine until two days ago, because suddenly I could not open them anymore because I always receive this error message:

CodeIgniter\Session\Exceptions\SessionException
Session: Configured save path "D:\xampp\apps\prototype\writable\session" is not writable by the PHP process.

If you create a simple PHP script in the CI app folder, that simply attempts to create a file in that directory, using fopen() or something similar, does that work?

-joho