Since I don't know how to get past the wrench in copying a debug, here's an easy recipe to reproduce the error.
1. Open up a fresh image of Cuis, and a fresh browser. 2. Add a dummy category and class. 3. Add a test method to return a string. 3. Add text to the string before accepting it. 4. Repeat 3 or 4 times then an error will appear: 'Instances of UndefinedObject are not indexable' 5. Clicking on the text pane will produce additional errors with the same message.
This appears to be semi-random. I have had it happen without the repeats in step 4. It sometimes goes away for a while.
To insure reproducability, I copied text each time from http://www.biblegateway.com/passage/?search=Matthew+1&version=KJV
In my newbie opinion, it looks like it must happen to people frequently. It also happens in Workspace.