about NMG ctbram helped me..though i could not deciphered wht he said..i might help u...let me know if u had figured it out!

ctbram said:
Non-manifold geometry - If cleanup messes up the model. Try using the polygon select tool, checking for NMG. It will highlight the problem and you can try to manually fix it.

In many cases the only real solution is to delete the offending region and simply remodel it.