U3's Couch

Please verify that the receive location exists, and that the isolated adapter runs under an account that has access to the BizTalk databases.

This error occurs because the web service is running on the application pool which security account user is not a member of the BizTalk Isolated Host Users group. in order to solve this error, you need to add the user that runs the web-service into the BizTalk Isolated Host Users group. Or change the application pool to the pool which user is already a member of the BizTalk Isolated Host Users Group. :)