Out networks is built by 6506, 3750 and 2950 swiches. For some weeks ago all uplink ports in the 2950 switches went into error-disable caused by loopback-detected. The strange thing is that none of the 3750 swiches where affected even it the same vlans are wide spread all over the different type of devices. Does anyone know if there are some bugs in this 12.1(19) software that triggers loopback-detected???