Connection to Steam lost Exiting -HELP-

[xpupx]

I know other people are having this problem but I have not found a solution for it yet!
I am unable to create missions because when I go to test them in multiplayer I get the following:
Connection to Steam lost Exiting
Server failed to connect to steam
Firstly I never had this problem until the last steam COD patch of maybe it was a Steam update that caused the problem not sure!.
Secondly it is unlikely to be hardware specific as I have just replaced my Main board recently and still have the same problem !
And yes i have all the latest drivers and windows updates.
Any help would be much appreciated.
Regards
xpupx