F5 APM Office 365 SingleSignOut

Hello. I am having a problem getting singlesignout working from office365 (singlesignin is working fine). I specified the LogOffURI parameter in the Set-MsolDomainAuthentication cmdlet to https://APM-VS:445/vdesk/hangup.php3. The session gets removed from APM but the user is redirected to a page that says:

This should not happen! Internal errors!

Any ideas? Thanks.