It's happening on some clients with the two L2JGuard files, we've found out that but at their support Skype when we let him to know that what's the problem he simply keep the message unanswered.
If we set the debug mode on, the protocol on an working system when selecting a gameserver is, for example, 273, when the issued user put the two .dll files protocol version switch to -2 and goes fucked as hell, we've having over 20-30 issued users.