Strange ZModem behaviour

[Axel Dunkel]

I am having trouble with high speed zmodem uploads to an UNIX Sys V R3.2
system: even at very low system loads the transfer suddenly hangs and breaks
down...and after a few minutes, when both sender and receiver gave up,
there is no chance to even start a new transfer, you have to logout first!
Strangely enough, "stty -a" does not show any changes.
Does anyone see something simular before? I am using a specialix SI/8 card.

Thank you for any suggestions..!
Axel  (ad at cat.UUCP or ...!unido!cat!ad)