the debug log is helpful. It should show:
Connected by address:
(N times) Testing transfer:
if N equals 0 it gives: No valid presentation contexts found and hangs up.
This means that either the sending server gives out no transfer syntaxes, or that the receiving end maybe muddles up the list processing e.g., while reading dgatesop.lst (which I believe is reread very often).
You could try for a test to remove dgatesop.lst from the receiving end: this will cause conquest to accept anything from anybody.