100 mb Full duplex on fiber connection

I have a fiber link between 2 buildings (distance approx. 500 meters)

3com superstack II 3000 on one side and HP2424M on the other. Problem is I can't get 100 mb half or full duplex to work properly. Roadkil's Comtest shows an 9000 kb/s out but the bytes in's stays below 50? I tried to set both sides manually of course, but I get the best results by setting it to 10mb half duplex 468/1144.

Thing is that I need to copy a 6 GIG Oracle dump file nightly between the two buildings and I need the speed 8-)

Anyone can shine a light on my prob?

Thanks in advance,

Mike