Thanks for your help still doesn't work.

I have tried the following things:
Cleaned mesh with everything on.
Cleaned mesh with only non-manifold geometry on
Cleaned mesh before I put them togeather.
Put a selection box around the whole mesh (in vert) and hit delete
Used constaint tool

What I find strange.
I can convert is easily before the combine and can't after. I can convert both before

Again thanks for your help

Wader