Error: Your request can't be completed right now. Please try again later.

I have MS Exchange 2007 - 2013 CU3 coexistence at two sites connected by VPN link. 

OWA and Outlook work fine for mailboxes on 2007 server. OWA does not work for mailboxes on 2013 server, however Outlook connects fine to any mailbox on 2013 server.

Here is what happens with OWA.

Users (Moved from 2007 or Created on 2013) can log in to OWA and see their mailbox folder structure and messages, but when they click on any email they get "Error: Your request can't be completed right now. Please try again later. " instead of the message body. When they try to create a new message via OWA, GAL lookup does not seem to be working, everyone gets "Error:The message can't be sent because at least one recipient isn't valid."

I can't see any errors in the application event viewer that get logged during OWA session.

HTTP Log has the following error codes: 241,242,302,401,403,405,500.

I am not sure at this point, but I think 405 is the HTTP error that can be associated with errors displayed in OWA

date                         11/28/2013
time                         18:01:02
s-ip                          192.168.1.1
cs-method                POST
cs-uri-stem               /owa/service.svc                           
cs-uri-query              action=GetConversationItems&UA=0 
s-port                       444 
cs-username             DOMAIN\chukcha           
c-ip                          192.168.1.113
cs(User-Agent)          Mozilla/5.0+(Windows+NT+6.3;+WOW64;+Trident/7.0;+rv:11.0)+like+Gecko
cs(Referer)              https://EXCHANGE2013/owa/#path=/mail

Any suggestions on troubleshooting this problem?