Bad Request 400 when Opening Options in OWA (ECP)

Sometimes there is the problem that with Exchange 2010, that a Bad Request 400 Error appears when OWA is accessed the first time. The issue is related to the ECP/Options part of OWA.
When you first access OWA you’re asked to set the language and time zone settings. After clicking ok a Bad Request 400 error appears.

There are several solutions available for this issue:

• Delete OWA and ECP Directories and Recreate them
• Set the language and time zone settings before you access OWA over the Exchange Management Shell:

  Set-OwaVirtualDirectory -identity "SERVER\Owa (Default Web Site)" -DefaultClientLanguage 2055
  Set-OwaVirtualDirectory -identity "SERVER\Owa (Default Web Site)" -LogonAndErrorLanguage 2055

• Disable and reactivate Outlook Anywhere

In my case these solutions didn’t work. So what I did to resolve the issue on these few affected mailboxes was a mailbox move to another database. After that the issue disappeared.