Hi Joe,
Sorry for the inconvenience. You can fix this immediately by adding this on the ScriptLoader control in layout.master
IncludeAspTreeView="true"
This was caused by my efforts to reduce the amount of unnecessary javascript. I " thought" the TreeView only needed the javascript if it had the ShowExpandCollapse="true", so I backed it out by default and only added it if the TreeView was configured for ShowExpandCollapse and it seemed to work fine in most cases, but I didn't find this one.
It seems if the calendar does a postback with the treeview on the page it causes this error, so it only happens in skins that use a TreeView menu. In any case, I knew that such a change might have some side effect that I hadn't expected so I made sure there was an easy way to turn that script back on as indicated above.
Best,
Joe