If you can open the QVW file you can try exporting the layout and then importing it into a new document.
If you can't open de file you should try opening it without any data, go to the start page, recently open documents, right click and select option "open without data".
Using Len(field) > 0 instead of Not IsNull(field).
Did you try to enable log files? Maybe the you can get more details on the point where your script if failling.
To enable it, go to settings - > Document properties -> General Tab -> check 'Enable log file'
hope it helps