If you are like me and didn’t set Citrix XenDesktop 5 to trust XML services on install and are now looking for how the heck to change it…they do call it out in the documentation, although I had to export the documentation to a PDF and then search it.  Here it is for convenience:

Set-BrokerSite -TrustRequestsSentToTheXmlServicePort $true

In Citrix XenDesktop 5 in theory everything is now exposed via Powershell.  I love Powershell!