Unable to save - Permission error

Hello Captivate community.

I am running into the frustrating situation where a project which saves just fine all of a sudden gives me the error that I do not have permission to save the project any more:

I seem to run into this with big projects? Another client's project files sometimes do the same thing.

If I "save as" and rename the project, it allows me to save in the exact same location! And then it might save once or more as I work, before giving the same error...

I am working on Windows 10, Captivate Classic 11.8.3.8