That error comes up with (IIRC) all the 3.X releases, when the javascript is already in-browser but is unable to retrieve data from the radio.
So if you've logged into a radio and that later appears, it's basically telling you there was an error communicating with the radio. (Like the radio is unreachable on the network, session down, locked up, whatever) If you see that when you first try to log into the radio, it's almost always a sign that the radio is unreachable but the main HTML and javascript bits were already cached in the browser, so it attempted to build the page from 'memory' but subsequently failed to communicate with the radio.
The 'fix' is to find out what is causing the radio to be unreachable/unresponsive.