Someone else has reported that in another thread, too:
http://forums.winamp.com/showthread.php?t=375004
I can only suggest to visit the website of the radio station itself and open or save the playlist file from there. Although I always save the playlist files onto my PC (I do that in Mozilla Firefox), opening the files directly should work, too.
My own .m3u-file "Radio Streams 2012" is still working:
http://www.lastfm.de/user/SabineKlar...sts_for_winamp
But I have mostly only radio stations with my preferred genres in my long playlist.