I have a file (drawing) I am unable to save. I get the message "Internal diagnostic fault 43 error from 809." The drawing disappears on attempt to save and is unrecoverable without a computer re-start.
I just emailed you -- but in your post here I see that you are using v10; I had assumed v11 earlier. Have you tried doing a Layer Utility? This saves out the file as layer files -- and it saves all the GTV's and MSP sheets, as well.
Whenever there is a problem in a DC5 -- run a Layer Utility!