I know this is old and "Supposedly" solved, but I was just searching for a solution to this exact problem and this "Solution" didn't solve a thing for me!
So, I figured I'd add the TRUE solution here, in case anyone else stumbles upon this and needs ...
I have a 2960-S switch attached via GLC-SX-MM Multimode Fiber connect to a SG300-10MP switch. The SG is essentially unmannaged at this point, so telling the port on the 2960-S to not negotiate the speed was exactly the thing that allowed this connect...
