The file 'ABControl.tmp' gets created when the AB Tutor program is saving changes to settings, groups, policies etc. 

It first creates a file called 'ABControl.tmp' and saves data to it, backs up the existing 'ABControl.xml' by renaming it 'ABControl.bak' and then copies 'ABControl.tmp' to 'ABControl.xml'.  This technique for saving files is standard so it anything goes wrong when saving to file the original 'ABControl.xml' file does not get corrupt.

There are two reasons you may get this message:

The file for some reason has been made 'Read Only'. If so, just delete this file.

The user running AB Tutor does NOT have access rights to create/save files in the correct folder.

Windows 7/8:   c:\program data\ABTutor\Tutor

MacOS:                      /etc/ABTutor/Tutor

If you use AB Tutor access passwords and you restrict the teachers to have Tutor level access only, then they cannot change the system settings or groups, etc and so the system will not try to save them.