Chris,

There seems to have been an issue with the install order b/n Vegas 6 and ACID Pro 5 due to the Media Manager v.2.0 being a shared component across the apps (and ACID Pro 5 using the older MM v.1.0, while accessing MM v.2.0 thus resulting in this particular error).

It's been resolved in ACID Pro 5.0b that comes with MM v.2.0.

Since you're getting this error in Vegas 6 that's been using MM v.2.0 from the get-go, there's still some 'sharing violation' with an older MM version there somewhere. If installing the latest builds of all your apps won't fix that, try changing your Media Library's folder/path.