Based on the error message that Google is spitting out and my experiments... here's what I believe is happening.

One or more PCs connected to the Telkom network, most likely attached via ADSL are infected with some sort of worm that is targeting the Google block of IP addresses. They have therefore blocked (probably automatically) the IP addresses from which the attack is coming.

The problem is that the ADSL IP addersses are dynamic and I as a "good" user can easily end up with an IP address that was doing "bad" things yesterday. That leaves me up the creek.

I installed a proxy server on one of my company's server installed at UUNet and routed my web traffic throught that and Voila! problem solved.

So my guess is that Google has denied access to a large chunk of Telkom / ADSL IP addresses and we can only hope that it's a temporary measure.