Hi
I keep getting this message which completely locks my computer up for about 5 minutes each time.
There are only 2 boxes to tick, Exit boinc and Cancel but neither seem to do much good.
I would suggest a 3rd button which disconnects the internet connection instantly as if it cannot sort it out with the client in a few seconds it should be terminated
if this cannot be done perhaps a warning not to chuck a brick through the screen in frustation should be included.

The 'client' is the hidden (worker), part of BOINC. It's THIS that the manager, (gui), is trying to communicate with, NOT the internet.
The port used is 31416, and it's possible that your firewall is blocking it.

(And if you want a button for disconnecting BOINC from the internet, it's called No new tasks, and resides in the project tab for each project that you're running! And it's been there for years.)

PS
You asked about the same thing in this thread on the 4th October. Did you read the replies? (They implied a different problem and solution, which may be more correct.)