Hi there, this isn't really reproduceable, but I thought i'd post it in case anyone else has come across this problem, and can shed some more light on the cause.
in version 6.0c, i noticed that some of the media was missing from the project media list. further, when i tried to drag something into a bin, nothing happened. the search function was also not working properly. finally, i tried to import a quicktime movie into the project, but it wouldn't take it.
I saved the project, quit and restarted vegas. now everything works again.