jsonrpc.js timing out

When I bring up my web browser and point it to my Media Server 7.7.2, it usually just hangs until I stop it and reload the page, then it finishes. Firebug says it's waiting for a POST to jsonrpc.js, which times out after five seconds, retries, then keeps timing out. There is nothing interesting in the server log.

Is this a known problem? Is there a fix?