Ah! I now re-read your last comms. Other projects in the SAME version/build of Vegas are working as they should. OK. Then we need to accept that there is something icky ( tech-term that!) with this ONE veg.

1] - Can you copy and paste ALL media to a NEW instance of Vegas?

or ..

2] - Can you SAVE project under a new name and reopen?

Just try these 2 potential remedies out against my "icky" theory for me - please?

The other thing you might also try is to locate your Vegas 7 TEMP directory and see if you have any dormant, old and mouldy TMP and Undo/Redo buffer files in there? You may have a Undo-"challenge" command lurking and seeking its once-know parent - yeah?

I must say, this has been the single most clearly visible benefit in going to V8. The Temp directory appears to be behaving much better. Of course this might be a local benefit for me. But yah never knows?

Grazie