Hi LowTide, Sorry for the delay.
Version
4.4 of DayPilot includes a fix of a bug that prevented the calendar from working when it was first loaded with Visible="false" and than activated during a partial PostBack by setting Visible="true". If you are not using 4.4 I would try upgrading first.
If that doesn't help, can you please contact me at daypilot @ annpoint.com?
The problem might be in the Tab control (although after a quick look it doesn't appear to do anything else then changing visibility of the divs after tab header click) or in the AJAX update of the grid. I'm not aware of any bug/limitation that would prevent this scenario.