The server I play on (VOLCBAT) have now got a ban on the XAM mod. XAM modded players end up crashing the server and forcing it to restart. The only reason we can think of is that the XAM mod modifies damages and such.
XAM mod also enables the M16A2 to have a fully automatic firing mode, which is not hardcoded in the original game.
We testing this out, I shot a guy with a fully automatic M16 on and the server ended up crashing. Reason:-> Client says 16 bullets on ya head very quickly, Server says that not possible as single or burst rate is not that fast.
We also reackon that the damage modifications crash servers too, e.g. a RPG into a tank will have different damage amounts between server and clients ending up in a crash, although we haven't tested this.