Customer attempts to copy a large file from a server in an IPS protected vlan to a host in an IPS un-protected vlan and the copy fails if file is greater than about 2Gbytes in size. If the server is moved to the un-protected vlan the copy succeeds. There are no events on the IPS suggesting any blocking or other actions.
There could be some normalizer engine events which can drop/modify traffic without firing an alert. Some of them seem to be on by default. Could you try enabling "produce alerts" on the normalizer signatures with deny or modify actions?
Another way would be to put an event action filter for the source or target (or both) and filter out all deny actions. In that way, you are telling the sensor do not block any traffic from or to certain IP address (based on how the filter is formed). I would use this filter to cover all signatures and sub signatures for the source/target in question.