Well, I don't really like the way that YMIR goes - to send a packet to the server that just sends a packet back with no information. You could just call the function of the interfaceModule "AskSafeboxPassword" and remove the check to be near of the safebox npc (which you've already done) so it will be faster and without unnecessary packets. For this you've to give the uiInventory a handle to the interfaceModule (just create a variable in the uiInventory called "self.interface" and refer this to the "self" variable in the interfaceModule after the interface creates the inventory) and call the "self.interface.AskSafeboxPassword()" function. This way that you told does work but it's not very nice..
Anyways, thanks for the release.
Kind Regards