I'm a little baffled with this one...
I connected a 3560, using an SFP GBIC and SC to LC Fiber cable, to a 4912 switch - worked fine. I disconnected the 3560 from the network for reasons not relevant to this discussion.
I connected the same 3560 with no config changes to the same 4912, using the same GBICS and Fiber cable cables. This time I get a "errdisabled link-flap" error on the uplink interface. I changed the speed on the interface to 1000 full and re-enabled the interface. The interface came up, but on the 4912 switch - the config shows that the interface is not connected.