Okay, I finally managed to fix my error.
For future reference - if anyone stumbles upon the same mistake - follow these steps
- Turn on debug in your config file
- Localize where the error occurs (in my case, it was when I tried to access /panel)
- Insert following into the file, where the error occurs:
session_save_path(sys_get_temp_dir()); - Save and upload
That did the trick for me!
Thank you all for your inputs during my error-finding
Best regards
Aris Kuckovic