Virtex4 MGTs using Aurora Core

Hi,

I am having problems trying to get an Aurora core working in Virtex 4
parts.
Has anyone managed to get an MGT working in Virtex4?

I am using Aurora 2.4 and just trying to do a simple loopback between
2 MGTs. I can't get CHANNEL_UP to assert in the Aurora cores and
the MGT is showing RXBUFERR indicating an RX FIFO underflow/overflow?

I have followed all the clocking recommendations in the MGT User Guide.

Any thoughts?

Thanks
Dave.