There might be many reasons for the above error, but here’s one we couldn’t find anywhere else.   We had a licensed copy of Windows 2008/R2, then realized we could save a license and use our MSDN subscription on this developer virtual machine.  So my worker upgrade to the Enterprise Developer edition.  That seemed to mess with BizTalk’s registry settings.  The secret to fix the above error for us was to run the BizTalk install and select the “repair” option.