Thanks Kurt...
I have tried what you suggested and it works, it get converted into SubD, but my vertices are now breaking up big time ...Especially around the eye.

It looks like my poligons couldn't get converted because My base mesh was containing too much vertices that didn't need to be there...I guess!
The Script editor ask me to go to Polygon>Clean up which I did and it highlighted two faces around the eye.

Should I re-try modeling the head and make sure that I clean up properly the vertices ?

Cheers