Check if there is a pattern, does it occur every time you perform a particular operation? Is it intermittent? Does it persist after a fresh start?
For example, deleting styles in a range in Project Style management consistently gives this error. It is most likely a Map Maker bug.
If the problem recurs persistently, but there is no pattern and restarting Map Maker doesn’t work, try turning your computer off for a minute and restart it again.
Check that you are not trying to do something silly (like loading a project from a different application).
If that doesn’t seem to fix it, try simplifying your project – have you got a guddle of data layers that you don’t really need?
If possible, try re-creating your project bringing in your data, any .tif layers etc. and refreshing your styles.
Finally it could require re-installation of the Map Maker program, or possibly an update to the Windows operating system.