During the phase of coexistence with exchange 2007 and exchange 2013 the access to OWA service is handled through a redirect, in a nutshell the 2013 exchange becomes the service access point and, once the user has entered his credentials, If the mailbox is still on 2007 the browser is redirected to the legacy.domain.com address (legacy is just a label) that should point to owa 2007.
It may happen that during this redirect the user receives an error despite the virtual directories configuration is correct.
This is the shown error:
X-OWA-Error: Microsoft.Exchange.Data.Storage.NotSupportedWithServerVersionException
Fortunately it's not a configuration problem on the server side (Fortunately or unfortunately… it depends on the number of clients on which the problem occurs) but it is a problem of the client cache, so instruct the user to clear cache and cookies, try again and everything should work fine.
