I am trying to complete my Exchange 2007 to 2013 upgrade. Mail is flowing for all my 2007 users. OWA redirects nicely to the "legacy" site. However, when I try to log into OWA as a new 2013 user I get the "something went wrong" page. What is noticeably wrong is the "time stamp" on the error is exactly 4 hours off from the current time. When you show more details it says:
X-Clientld: GOPY - N0EW -KJRE - XCJXW
X-FEServer: MYSERVER
Date: 8/8/2015 6:21:21 AM
...when it is "only" 2:21:21 AM