Is this a bug?

[Doug Heffernan]

The only thing noteworthy is that on the test site, the calendar was not activated

This is kind of important imo, because that error is being logged when, as per your post above,you  put a few dates in the calendar. Can you activate the calendar at the test site as well and perform the same action that you did at your main forum and see if the error will be logged in there too?

[DenDen60]

For one reason or another, it stop. I am not sure but it might be link to the calendar some how. I will have a bit more time in the next few weeks so I should be able to test it further.