My Work flow:

Source video = ProRes HQ QuickTime file stored on a Fiber attached XSAN
I drop the Quicktime file (stereo audio) into Sound Track Pro.
-Adjust audio levels and do some mild dynamic compression

Choose "File/Save as" and ad an "a" at the end for the file to signify new audio levels

Confirm that the file needs to be flattened.

STP goes through the saving process and at the end I get "The Document "XXXXX" could not be saved as "XXXXFilenameIselectedXXX"

There seems to be no logic or pattern as to when or why this happens. Anyone got any input on this?

Thanks.

Are you trying to Save to the XSAN? What happens if you try to save locally?