Make sure that you are using the right internet, (Cable, LAN, etc..) selection in your prefrences! But if it says "Masterserver Timeout" or "Masterserver failed" it may be your internet connection. Make sure you aren't downloading anything that's taking up your banwidth. Other than that, if your trying to connect using a third party mod. (Like trying to connect while using ChaosUT conversion.) or if your searching for a game under a certain tab that got added when you installed a mod, those usually don't work because they don't have a backup .ini stating the type of prefix it should look under, leaving it blank. Worst case scenario, just re-install ur ut leaving all the extra folders including system, texture, sound, and music that way you can keep all of your dl'ed mods.
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Worst case scenario, just re-install ur ut leaving all the extra folders including system, texture, sound, and music that way you can keep all of your dl'ed mods. 
