isl trunk on 6509

[whitaker]

I  was trying to set up an ISL trunk on my gigabit fiber link, but it responded that it was only able to run in nonegotiate mode.  Since this is going between two 6509s gigabit fiber link, I was never able to exchange VTP information between the two in nonegotiate mode, and it wouldn't let me switch it to anything else.  I now have a trunk running across one of the 10/100 switch module ports.   Is this a limitation of the gigabit fiber links?  Or is there something I'm missing here?