to narrow this down even more...
1) Change a combobox in which autopostback is true
2) Quickly click the popup for the RadDatePicker
3) Page posts back, dates are unselctable on the calendar
4) Only way to get it to allow you to select a date is to change another field with autopostback
I tried putting this in the page_load, this closed the popup but it was still unselectable on the postback
fldDateofLoss.DatePopupButton.ViewStateMode = UI.ViewStateMode.Disabled
Anyone know what to try with this?