I found a repeatable REASON why I was getting this message. See if you have the same results:
Concise problem statement:
Steps to reproduce bug:
1. Click in a meta data field of a clip and make a note (i.e. description or comment). Do NOT press enter or return.
2. Use the mouse scroll wheel to scroll up or down; or use two-finger scroll on magic trackpad.
3. Adobe reports "An Unknown Error occurred"
Results: Premiere Crashes
Expected results: Premiere to NOT crash!
If you type a meta data field and hit return, the error does not occur.
Premiere Pro CS5.5.2
Using DV footage (converted from Cineform using Adobe Media Encoder)
I did that too, but sice other users may experience it I wanted them to help me troubleshoot if anyone else had the same experience.