On a computer I've used for quite some time, I've started getting this message in the communications window:

Primenet error 30: CPU not registered
ERROR_UNREGISTERED_CPU
Retry count exceeded
Visit forums for help ...
Will try contacting server in 70 minutes

After 70 minutes, it gave the same thing. This may have been going on for hours.

I have three other computers running on Seventeen Or Bust - I checked two of them and they don't have this problem.

How can it be fixed?