Not sure there is anything I can do to help you as it doesn't happen to me (can't reproduce it) and you're the only person I've heard this happening to. Sorry.
Best thing I can suggest is the usual troubleshooting:
1. White list folder in antivirus.
2. Disable DEP protection in Windows or add an exception for the game.
3. Reinstallation, etc.
Nothing I can really look into without it being able to reproduce it.
The whole only happening after the second online patch is entirely coincidental as well. The update to online.exe was ONLY to online.exe and an attempt to address an issue another user was having with the launcher. It did nothing to the game code and only affected the launcher.
I didn't uninstall any clients for other servers or anything. One of the weirdest things that makes me think it's not a DEP issue is that songs seem to play fine when other people play them, but the game crashes when I do it...
That doesn't make any sense, though. Same packet is sent either way, to play the music. The only thing that is different is that it shows you a message using a regular PSO packet (Send01) about how much Meseta you have left after playing a song and that shouldn't crash your client. That's really strange.