Yeah as r@nsid has said, run a cleanup on it. If Im corrects it in the Poly menu set under Mesh>Cleanup, then set it to Nonmanifold.

It will then hilite the areas you'll need to fix...

Any mesh will convert to a subd no mater its state as long as the geometry is clean and the max face count is the same or above that in the modify>poly to subd menu

cheers
Jay