It looks like your user profile folder was originally C:\users\marsp
In the registry, your user profile is still pointing to marsp, so that's where the game is trying and failing to save to.
If you're comfortable with editing the registry, run regedit
go to HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\User Shell Folders
Change the entry for Personal to C:\Users\Mars\Documents
go to HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\Shell Folders
Change the entry for Personal to C:\Users\Mars\Documents
Exit the registry for the changes to take effect.
Next time you run the game, it should now save to C:\Users\mars\Documents\GTA San Andreas User Files
Let me know if this fixes the issue.
You may want to make sure all the values for the two registry keys above are pointing to the correct location.