A problem occurred while trying to use your mailbox. Please contact technical support for your organization. – OWA / Powershell

When attempting to open a mailbox through OWA, I received the error:

A problem occurred while trying to use your mailbox. Please contact technical support for your organization.

To resolve this, in Powershell, I ran the command:

Set-Mailbox User_Name -ApplyMandatoryProperties

Source:  http://support.microsoft.com/kb/941146

Note:  You may receive an error if the mailbox is located outside your current domain.

Set-Mailbox : The operation could not be performed because object ‘User_Name’ could not be found on domain controller ‘fqdn.domain.net‘.
At line:1 char:12
+ Set-Mailbox  <<<< User_Name -ApplyMandatoryProperties

To resolve the above, you’ll need to specify a domain controller in the mailbox’s domain on which to target the cmdlet by adding the following to the end of the cmdlet:

-DomainController fqdn.domain.net

So, for example:

Set-Mailbox UserName -ApplyMandatoryProperties -DomainController _fqdn.domain.net