> Thanks for the "boiling-down" of your config file. That helped me to reproduce the error quickly. It only occurs if you have a date/time attribute which is hidden as a conditional attribute. This is a unusual combination, that's why I haven't seen that bug before. Actually some 
> JavaScript code checks the validity of the date attribute, but since it is conditionally not there, the JavaScript code crashes, which triggers the dialog box you see. It's now fixed in the repository.
> 
> /Stefan
> 

Thank you Stefan!
That works nicely now.
Apparently it was less work to fix than to isolate it ;-)

Andreas