Background: bought HL2 some months ago; installed it, connected to
Steam and set up account, and activated offline mode -- my home is in
Portland, OR and has internet, but I work in Seattle, WA and spend the
week in a place where I can't connect my PC to internet (this is being
posted from somebody else's computer).  Until recently, offline mode
worked just fine.

A couple of weeks ago, took my PC home to activate another program
completely unrelated to STEAM, but while I had it online I connected to
STEAM  for the latest updates, figuring I might as well get current.

Last night, tried to run HL2 for the first time in ages.  Game lists as
"100% ready" but when attempting to launch the game, it returns the
error message "This operation cannot be completed when STEAM is in
offline mode."

What operation?  WTF?  How can I get my game back?

stePH