The reason for the depreciated message is because AMXBans was designed to run on PHP 5.x. As of 5.3.0, PHP depreciated that function, hence your warning message. Either you can fix it yourself or you can wait for Sleepwalker to fix it.
I do not browse the forums regularly anymore. If you need me for anything (asking questions or anything else), then PM me (be descriptive in your PM, message containing only a link to a thread will be ignored).