Setup: I've been running DNN 7 (Community) and eventually upgraded to 8.0.3, on a Azure Web App for more than a year with no problems (this is a much longer story as this all started with DNN 3 running on an NT box way back in the day, but that's not important to this...at least I don't think so).  Normally, I've taken the usual back-up-everything-within-an-inch-of-it's-life-then-update-production-in-place-and-cross-your-fingers approach, but this time, I'd like to use Azure's Deployment Slot support so I can duplicate the site, files and DB, apply the update, do UAT, then flip the slots when everything's good to go.  

I've been trying to setup a slot for a V9 update with little success -- it's throwing a 500 with little or no additional info.  

I've covered all the usual bases:

• Slot created, cloning all the setting over to the new slot.  I've actually tried with with and without cloning them, so this is not an issue.
• The new slot tested with the default file. 
• All files from the production slot copied down to my local drive and then copied up to the slot's folders, with timestamps preserved and both both copies verified with Beyond Compare.
• The DB copied.
• The web.config of the new slot updated to reference to copied db.
• PortalAlias updated so the portal I'm using for testing is linked to the slot's url.

No go.

I know this isn't a lot of detail and I'm not expecting a solution based on just this email, but is there any fundamental reason why you can't use a deployment slot for a Web App running DNN?

While waiting for a response, I'm going to try to dig up the error details. If I can get them, I'll post them here as a reply.

Thanks in advance!