I've recently installed ~40 2960-X 48 port switches (WS-C2960X-48TS-L). The floor distribution switch connects to building distribution (4900M) via fiber SFP/cables. In several locations, some floor child switches have their trunk uplinks to the floor distribution connected via GLC-T SFP and Cat5e cables. I've seen on multiple occassions where the floor distribution links to the child switches go down ONLY on the links using the GLC-T SFPs. Both sides of the link don't report err-disable, just down/down. I don't know how to deal with this problem. Can somebody help me? Thanks.