I've had this this problem a few times now.
When I'm amending elements in plan (last time I was changing the material to By Catagory) An error message displays something like:
"This view has encountered an error & has to close."
When I double click on the level to reopen it all my elements are solid black.
Other than closing/reopening is the a solution?
Any ideas what is coausing this to happen?
Hope you can help