I cant get portal 1 to work in offline mode

[turret king]

Hi i have portal prob.

Evrything is as up to date as can be....it just wont play

All other games work but this one.

Even portal 2 worked and it actully uses the internet for coop.

I get error message "this operation cannot be completed when steam is in offline mode"


Please help this is going to drive me nuts if i dont get it fixed.


Thanks