Cryptic error message!
 

I've modified a form I've used in the past, filled in a lot and now I can't save because of this error message:

[IMG]http://img257.imageshack.us/img257/7189/errorae8.png[/IMG]

I saved my OmniOutliner document earlier without any problem, but I must have changed something. I think it might have something to do with the "Column type" inspector, as I messed with something there, then pressed CMD-Z (undo) as it messed things up and I wanted it back like it was.

The error message isn't very helpful, so I don't know what to do.
I'm using OmniOutliner 3.6.2 within MacOS 10.4.10.