Hi Vernon,
Can you step through the UFL in Debug once it's called? If it's writing to a .sql file, does the file get closed or at least saved after each time Crystal has the sql generated?
The error is pretty generic so I can't tell if the error is being generated when Crystal tries calling the UFL, opening the .sql file or saving the file. Again this brings me back to a locked sql file, possibly by Crystal or by your database.
When does your database, I'm assuming SQL Server, open the file and exec the sql? After all the reports are run or immediately after each report is run?
When you have the error message, can you open the sql file in Notepad or a text editor? That would determine if the file is locked or not.
Good luck,
Brian