Error message: You have been disconnected from the server. Reason: Unable to connect to Steam.

[IT625]

Since the 25th Anniversary Update, I get disconnected from Half-Life after two minutes every times.
Error message: You have been disconnected from the server.
Reason: Unable to connect to Steam.
I haven't changed anything in my settings, my firewall or my router.
Does anyone know how to fix this problem?

[Soma Somt]

This is caused i think by the new update, i had the same problem.
All you have to do is go to the game properties, then Betas, and then choose Beta-beta.
You'll be able to play the old version. this worked for me

[IT625]

Great. It Works!!! Thank you very much Gajlo :-)