Hey Michael,
.Net 4 Extended is installed and the 4 Client is installed and all updates have been applied to the machine.
I think maybe rather the problem is that the machine is on the bleeding edge of all updates, rather than behind, but it could be that something didn't take during the build.
QB Enterprise V11 was recently upgraded to R6 and they've added a bunch of functionality to the ODBC connection. .Net is updated to the latest rev and now the Sync Engine is at the latest rev. But, the QB SDK is only installed to 8, and the latest Rev from QB is 10, I believe.
Of course if that was the problem, someone else with Ent V11 would also have a problem, although they may not be installing from a fresh install and updrades to the listener, etc. work just fine so it hasn't appeared.
There must be a way to poke around and check to see that the QBFC8 is installed and functioning. I can also try installing the Sync Engine to a client PC that also has QB Ent V11.
Hmmm.....