Hey George,

Definitely sounds like a network setup problem as opposed to a server problem as such - as to exactly where in the network well there in lies the problem.  dopostback does some fancy stuff - but in reality its just a call home function that sends the server a form request post.  The server captures this, handles the request and returns an updated page.

I have seen a problem something like this in the past - about 4 years ago - and at the time it was a proxy router that was incorrectly configured on the server.  I would raise a ticket with your hosting provider - detailing the ip addresses that you can verify are having problems accessing your server.

Westa