Have you tried removing the NICs from device manager then do a rescan? Maybe after being prompted to reload the drivers from that point it might resolve the issue.

 

Of my three PE2950s, two installed the new Broadcom drivers just fine, the third required an uninstall of the old drivers/tools before the upgrade would succeed.  I backed off VMWare server and some other things I thought might have been interfering, but in the end it was the network drivers.  Very odd.