this worked for me when I got the "Steam UserID Ticket Error" - but this should work for most steam errors.

Exit Steam completely, then delete the following files:

Steam.dll
SteamUI.dll
ClientRegistry.Blob

These will be found under your Steam installation directory - by default, this will be C:\Program Files\Valve\Steam\ (this may vary if you specified a different installation folder, or if you have moved your Steam installation).

I did that and then restarted steam and the error got fixed.

Yay!