Hey guys first time poster had the same problem as you guys. Just stumbled upon the solution for me. I use XPand not Steam and it seems the stupid editor creates and saves the file in the wrong place.
I have reloaded it a few times but I don't think that is the problem. I think the editor program saves them in a place the game doesn't recognise.
There are actually three config files I deleted one. (I don't know if you need to or not - probably not).
C:\Documents and Settings\Admin\My Documents\Sports Interactive\Editor 2010
C:\Documents and Settings\All Users\Documents\Sports Interactive\Editor 2010\editor data
C:\Documents and Settings\All Users\Documents\Sports Interactive\Football Manager 2010\editor data
the last one
C:\Documents and Settings\All Users\Documents\Sports Interactive\Football Manager 2010\editor data
is where you copy your XMLs to from C:\Documents and Settings\Admin\My Documents\Sports Interactive\Football Manager 2010\editor data
It's probably Windows ridiculous root system to blame but I had three differently named XMLs and I shifted one to C:\Documents and Settings\All Users\Documents\Sports Interactive\Football Manager 2010\editor data
and shifted one to
C:\Documents and Settings\All Users\Documents\Sports Interactive\Editor 2010\editor data and left one in C:\Documents and Settings\Admin\My Documents\Sports Interactive\Editor 2010 then I loaded the game and the drop box finally appeared.
The only option was [default] but I ticked or unticked change ( I can't remember) and the next screen had Matt2 (the C:\Documents and Settings\All Users\Documents\Sports Interactive\Football Manager 2010\editor data version).
I hope that is a help because it was doing my head in. Enjoy.