This control was not created correctly

With 2015r3.1 (Mac) I have started getting this Javascript error message:

I can make it happen 100% of the time with a calendar container control that i was using fine in 2015r3, if I copy that control and paste it into a new project.

Any suggestions as to how to troubleshoot this? It’s driving me nuts.

On the plus side, I like the fact that the Black Javascript Dialog of Death is no longer behind other controls on the page.

I should add that the calendar container in question works fine in the project in which it was built; it’s only when I copy it and paste it into a new project that it fails.

I just ran into this. I copied a Web Page from one Project to another and got an ‘UnsupportedOperationException’ that stated ‘This control was not created correctly.’

I quit Xojo, relaunched, and the project ran. That’s really strange.