A problem occurred while you were trying to use your mailbox

We had moved a user from Exchange 2003 to Exchange 2010. They couldn’t login to Outlook Web Access (OWA). They got the following error - A problem occurred while you were trying to use your mailbox.

It turned out the users mailbox was in the wrong region. Use PowerShell to find what the setting is.

This was a working mailbox.

Get-MailboxRegionalConfiguration -Identity user.a | fl

RunspaceId : 150e4a54-80d7-4ac8-ba45-2bddbbad1903
DateFormat : dd/MM/yyyy
Language : en-GB
DefaultFolderNameMatchingUserLanguage : False
TimeFormat : HH:mm
TimeZone : GMT Standard Time
Identity :
IsValid : True

This was the user with the issue.

Get-MailboxRegionalConfiguration -Identity user.b | fl
RunspaceId : 150e4a54-80d7-4ac8-ba45-2bddbbad1903
DateFormat : M/d/yyyy
Language : en-US
DefaultFolderNameMatchingUserLanguage : False
TimeFormat : h:mm tt
TimeZone : GMT Standard Time
Identity :
IsValid : True

To change it back to en-GB you run the following PowerShell command.

Set-MailboxRegionalConfiguration -identity user.b -Language en-GB -DateFormat “dd/MM/yyyy” -TimeFormat “HH:mm”

User could login fine after the change.