The only way you can use private server version 6.2.4 is use older versions of bot with full subscription NOT private server subscription. You can find old versions around the forums if not try asking Droidz directly if he has 1 for your version saved around. If you get problems with it you can't expect official help because older versions (exept tbc, wotlk, cata, mop versions that have their own forum category) aren't supported