Not sure what came of this problem. But ever since I changed my web application running the calendar to .NET Framework 4.0 it now gets stuck loading upon a postback after the event TimeRangeDoubleClick has been executed.
The calendar is inside an UpdatePanel, and at the end of the event I do (which is how I got it to 'refresh' the calendar data on a postback):
1. Calendar.DataBind()
2. Calendar.Update()
When running the application in Firefox with the Developer tools, I get no errors, not even with Javascript. Then I tried it with Firebug, and same results, no errors at all. Again, this wasn't issue prior to change the application to .NET Framework 4.0
Thanks.