We have Dell PCs GX270 with Intel PRO/1000 MT running Windows XP SP1 connected to a 3500XL-EN Cisco Switch. The problem is that when both switch and PC are set to 100 full duplex the PC can not connect to the network, either Active Directory or NDS (Novell Directory Services). The switch shows a LINK-FLAP error continueously and the Proset desktop software shows the link constantly changing from 100 full to 100 half duplex, even though as stated both ends set to 100 full.