Users can't delete emails and other tasks in OWA on Exchange 2010 SP2 RU4

Lot's of talk on the internet about this problem, most of which from a year or two ago.

I have a new SBS 2011 Server, fully patched with Exchange 2010 SP2 and RU 4.

Users complaining they can't delete emails from OWA main page (you can delete if you open an email and delete it), same with tasks, and can't move emails to other folders.

I've checked most everything that other people have said was their problem.  (ie., I don't have a host name in any of my bindings, etc.).

I'm up to the latest RU for Exchange 2010 SP2 yet the problem still exists.

I'm blind from reading hundreds of posts!  Is there an ultimate fix for this??  

Thanks.

(btw, I get this error in the event log when a delete is attempted):

Outlook Web App couldn't connect Exchange Web Services due to a configuration error. Response code = "500".