boot camp must update system software help

I recently updated to ML then downgraded to SL

I wanted to install Win 7 using bootcamp.

When i click on bootcak v2.0 it says must update system software?

I ahve a mac pro 2.8 intel xeon (mac journaled) no partitions.

for now I am running a trial of parallels but would like to be able to do it with bootcamp

can anyone help please