I confirm this as well. A few more details:
a) fails to play anything: music, audiobook, some audio jokes, sounds extracted from movies, anything. Both Free and Pro versions are unable to play any MP3 stored on the phone,
b) when you go to currently selected file details screen, you can clearly see, that Winamps reports that song length is 0:00 (0 minutes, 0 seconds); so I'm not sure, if the problems are caused by playing engine or are just due to incorrectly reading file length,
c) going back to previous screen is not the only effect; many times Winamp quits, going back to system (launcher) main screen; it is still available in notification bar, but any operation results in either quiting to the system or going back to previous screen,
d) happens not only, when attempting to play any file, but also when going through all files, using >| or |<,
e) as LooNaTiK said: reinstalling both Pro and Free version brings no effect; as well as restarting Android.
And at last, my private opinion. @Rocker: What are you talking about? You have hundreds of thousands of Pro users, that paid a few bucks for Pro version and you can't afford for ONE Galaxy Nexus, to test your PAID software on 4.1 JellyBean version? Don't make me laugh really hard.
I fully agree with mucdude! Current situation would be not acceptable for any free version. An as for the fact that hundreds of thousands had paid for this app and can't use it at all for over TWO WEEKS I have absolutely not comment. This problem should be fixed within 1-2 DAYS, not weeks!