Yes, there are PVP toggles out there. Some will turn your pvp on, but won't allow you to switch back and just gives the internal error thing. Anybody?
http://dl.dropbox.com/u/51448919/Projects/Java/TogglePVP.jar Commands: /pvp on - enables PVP. /pvp off -disables PVP. Config: Default: true - Set to true if you want players to have on default pvp off, false to have pvp on. No permissions. Tested on 1.1-R4