Sunghwa Jin огласил прекрасный список того, почему DestinationParty resolution may fail. Особенно обращает на себя внимание ответ на его пост от Amando Resendez. By default, as far as I remember, both BizTalk hosts run at account - e.g. without domain name. Never mentioned in documentation, hovewer, it's so critical - to run both IIS app pool thru which HTTP receive location will authenticate incoming requests and BTS IsolatedHost. Secondly, I forget this completely (because SSO?) - HTTP send port must use authentication for outgoing requests as well. By default it is configured to use anonymous. Although this happens after DestinationParty is actually resolved, it is also important.

Put attention : authentication trusted flag on BTS host means that MessageBox will adopt the messages not only from the account that runs such a host.

P.S. Some configuration details, for example:

HTTP receive location URI - /PBossReceive/BTSHTTPReceive.dll?PBoss (and receive port must require authentication.

HTTP Send port URI (for partner inbox) - http://<servername>:8080/StsWebReceive/default.aspx?PartnerId=PBoss&FolderType=MessagesInbox (and use Kerberos autnetication)