I think I also had this problem while using the very first editions of Abiathar.
Maybe your copy is out of date?
I updated it before i started.
Did you happen to change the names of any of the levels?
I added new levels as maps 0-32 , with maps 0 being Shadowlands, map 31 being the rocket from the orginal game, and map 32 being the credits from the original game. I moved all the original maps from 33-50.
What is your operating system version (e.g. Windows 7)?
Windows 10, and i never tried it on any other OS.
does the error occur if you just move one level? Does the error occur if you only change a tile or two and don't shuffle the levels at all? Have the folder's security settings been changed at all?
The error occurs the second time i save. The first time i save is when i name the mod. When i make anything with the editor and try to save, the error occurs and it doesn't save.
What is the full path to your Abiathar folder? For example, my Keen 4 files are in C:\Users\Ben\Documents\CK\Keen4. Please try making a new project in a different folder (maybe one whose path doesn't include any special characters) to see if that works.