I don't think this will be the problem but when you do a "Save As" make sure the file type is set to PLN.
A couple of times I have saved as a different format and wondered why the PLN wasn't updating.
If you can't "Save As" to your desktop then there is something very wrong.
Can you save from other programs or create a new text file or folder without any trouble to the same place you are trying to save your Archicad file?
If you can there is a problem with Archicad (all I can think is it is in demo mode).
If not then there is a problem with your PC / permissions.
Have you tried shutting down the PC completely and restarting?
Barry.
One of the forum moderators.
Versions 6.5 to 27
i7-10700 @ 2.9Ghz, 32GB ram, GeForce RTX 2060 (6GB), Windows 10
Lenovo Thinkpad - i7-1270P 2.20 GHz, 32GB RAM, Nvidia T550, Windows 11