Well i dont know about AOs server, but in my server ther are some "reserved" nicks that you CANNOT use.

the code is in the unrealircd.conf and looks like this:

/* Banned nick names */
ban nick { mask "*C*h*a*n*S*e*r*v*"; reason "Reserved for services"; };
ban nick { mask "*N*i*c*k*S*e*r*v*"; reason "Reserved for services"; };
ban nick { mask "*M*e*m*o*S*e*r*v*"; reason "Reserved for services"; };
ban nick { mask "*H*e*l*p*S*e*r*v*"; reason "Reserved for services"; };
ban nick { mask "*O*p*e*r*S*e*r*v*"; reason "Reserved for services"; };
ban nick { mask "*I*n*f*o*S*e*r*v*"; reason "Reserved for services"; };
ban nick { mask "*Admin*"; reason "Reserved for Administrator"; };
ban nick { mask "*IRC*op*"; reason "Reserved for ircops"; };
ban nick { mask "*Oper*"; reason "Reserved for ircops"; };
ban nick { mask "Status"; reason "Bug in mIRC"; };