There appears to be an incompatibility between several HP IE add-ons and the RadDatePicker (maybe others too, but the radPanelBar works just fine).
The behavior varies from the pop-up calendar refusing to pop up at all, to the calendar popping up w/all dates grayed out. Only two people (there are about 100 seats out there running my web app) have this problem and they can login to a neighbor's computer and it works great. One of the cases they are 100% citrix, so they are all really running the same copy of IE --that is when I realized it had to be a different or corrupted profile. Here is an excerpt from an e-mail from one of my customers:
There were four add-ons that apparently auto-installed themselves when I installed the software for the HP printer that is attached locally to Tracy’s PC. He disabled those add-ons and everything works fine now. Apparently they were conflicting in some way. I thought maybe you could use the information to help figure out the similar issue you mentioned with another customer.
The add-ons were:
HP Clipbook – Browser Extension
HP Print Clips – Browser Helper Object
HP Print Enhancer – Browser Helper Object
HP Smart Select – Browser Extension
Of course, I don’t know which one caused the problem, but I don’t intend to re-enable any of them.
We resolved the problem by unloading / disabling the add-ons, so I'm not asking for help. I just thought you would want to know for other support cases and also maybe fix this incompatibility if there's something you can do on your end or by contacting HP.