Couldn't post in bug section, so I'm putting it here.
There is a grenade pickup in San Fierro that, if picked up by the player, results in an instant ban:
(http://i.imgur.com/Y3KsCRf.png)
the grenade pickup.
(http://i.imgur.com/0xW4nBT.png)
location on the map.
This has either been fixed by Byrner and he hasn't updated the post or you have a mod that places the grenade there.
Fixed!