I dunno which tutorial you are refering to, but I don't think the Split Poly Tool will work correctly if you click in the middle of a surface like the center of a face. As far as I know, the Split Poly Tool is used by clicking on edges. You must first click on one edge, then click on an adjacent edge. Note that you cannot expect the tool to work if you are clicking on a second edge that has other edges inbetween itself and your first edge, so like you can't click on one edge, then another edge six faces away.

It's possible Mike was using a special tool, perhaps similar to the facePathSplit tool I have for download on my site which might need to be used differently.

Last, but not least, you might not be able to complete an edge with the Poly Split Tool because of extra faces you are not aware of that would actually make the geometry layout different that it appears. (like a face directly on top of a face) I doubt this is the problem, but if you want to check, try selecting random faces around your problem area and move them about to see if you can find extra faces underneath that shouldn't be there. (undo to return your geometry back to where it was of course after moving stuff around)