Half-Life won't play demos

Archived from groups: alt.games.half-life (More info?)

Just updated HL to Steam for the sole purpose of watching some
demos, but when I try to play them (viewdemo or playdemo)
the program stops responding. I know they're the right version
as other people have been able to view them, and HL reports no
error -- it says 'playing from demo bla bla' then just stops. I can
record and play a demo myself, but can't play any of the ones I've
downloaded. The only thing I can think of is that Half-Life is still
"not ready for offline play" (Still have no clue what that means
exactly). Got a few hours to go before it is. So should I bother
waiting? Is that the problem?