Can you add some code that handles the deletion of a data type that is already in use?  Perhaps, warn the admin before, or remove the data type from existing document types that use it?

I had the problem today.  I thought I deleted the data type from my exisiting document type that used it.  But after removing the data type, the document type would crash when I tried to access it.  No error handling in there at all, just an exception.  This makes it impossible to repair or delete the document type unless you go on a wild goose hunt in the databse (which of course is very difficult).

Thanks!