The question is, what is your server? Are you running Twonky on a PC? Perhaps you're running Windows Media Player? Or then again, perhaps you are using the server in your Network Attached Storage, which may or may not be Twonky? You could be using Serviio or Jamcast on a PC too. Perhaps you're using a Mac though?
First, try rebooting the server. Then, try rebooting the radio. Then, try resetting the radio to factory defaults. Then try clearing out the old 'detected' Evoke from the server list and redetect. I can't be more explicit as to how you manipulate your server as you have not given enough leads. You could always try resetting your server back to factory defaults (or reinstalling the server software) but that is kinda extreme. If that lot doesn't work, then post back here with a description of what you are actually using.
Running better than ever from my Twonky NAS media server. I'd swear this version had tweaked net code, but I have recently shifted channels so it may be that, but a week or so before the update so it still seems better. Perhaps I'm just imagining things.