Nope. All connection in the Dataflow are SQL Server.
I went into the "SecurityCall Staging" Transform Operator and blocked all inputs that don't have a corresponding field in the Write Table. I ran it again and it worked.
(????) Weird, since unblocked fields never gave me a problem like that in the past. But I have gotten odd SQL errors in the past, re-run the Dataflow, and then they disappear.