I don't know the answer to that but are you using rtpMIDI? that's what i've used b4 and works over LAN which is ridiculously fast compared to what you need for midi clock and it worked great.
also have you setup the midi clock correctly... you need a Preset called Clock in the controller manager and then either Midi Clock In or a Midi Clock Out on each computer. I've taken to adding both just in case you want to swap them around, also it's important to remember the midi Clock Play button is on on your Sending PC only not both.
i'm not trying to patronise you here i'm just preventing having to type all that anyway.
Peace dude.
my apc40 mapping for 2.5.0 is here if you have one of those: (no clock in it though)
http://forum.djtechtools.com/showthread.php?t=53026