Recently, we tried creating a secondary Isolated Host to separate receive and send processing for WCF. After reconfiguring the servers, we were faced with the "Receive location for address '' not found. (The BizTalk receive location may be disabled)". Puzzled, we looked around for configuration issues. After some reading (http://technet.microsoft.com/en-us/library/aa559328.aspx), we remembered a new isolated host needs a new application pool. Adding another application pool to the mix the the new host fixed our trouble... Jotted down for posterity ;-)