Problems connecting to HTTPS websites on unsecured WiFi
The certificate is not trusted because the issuer certificate is unknown.


Given the google host, it is not very likely that the host itself is the cause of the error.

It sounds like there may be a SSL proxy, or some other form of deep packet inspection on the network. 

This may be a rogue agent, or a legitimate part of the corporate network. 

The idea is simple enough, each client has a root certificate installed for which the private key is known by the router or proxy. The proxy then acts as a "man in the middle" and decrypts and re-encrypts data on the secured connections. This allows the proxy to do a deep inspection of then content to and from external sources, such as https sites. 

Some may argue this is a bad thing, since the proxy (and possibly whoever has access to the proxy) can now see all the data that is thought by the user to be secured end to end. Some may argue it is a good thing since the corporate can inspect and verify, and protect itself against, data leaving and coming into the network before it reaches the end point. 

The other users may not be experiencing the same symptoms as you if they already have the proxy certificate source installed as a trusted CA, but the deep packet inspection is still being done. 

There are many resources in the internet covering this issue, here are some of the first hits covering this;

http://cookbook.fortinet.com/why-you-should-use-ssl-inspection/

And

https://en.wikipedia.org/wiki/Man-in-the-middle_attack


  "The page you reached is blocked for browsing!"


Given the above possibilities, I would suspect a firewall (or the proxy) is blocking you as well.