unable to ack - documents processed twice


I am having some problems with some documents, not being able to ack to the broker

the error is:

2011-08-16 11:00:02 CEST [ISS.0098.0049C] Exception:com.wm.app.b2b.server.dispatcher.exceptions.TransportException: Invalid Sequence Number (277-1773): Invalid sequence number was passed in.
while executing trigger. Unable to ack Document for TriggerStore:IBXBackend.customer.EBP50IMTMasterData.triggers:receiveTradingPartnerUser_EBP50IMT.

our environment consists of several ISes and only one node has this problem. however these documents are very large, and only handled by this particular server.

i can see that documents that have processed successfully have status UnAcked on the broker after this error is produced, and thus they are picked up again and processed again… causing problems ofcourse…

we are running 6.5 with broker 8.2 - we had the same issues on broker 6.5

any ideas would be appreaciated?