I had this same issue once, I even recorded a vid, but it's long gone cause it was like a whole year ago.
I was in Conn, dueling a friend on my Roc, and everything was working fine. I SNed a gun off his Virage, and after that -Nothing- did any damage to him. I still could damage myself with mines, and he could damage me like usual, but my guns and mines on anyone else didn't work.
It fixed itself after relogging, so I didn't bother reporting as bug.
