Cant connect remotely to mi Hard Disk

I have an external HD attached to my Airport Extreme and before my upgrade to Lion OSX I used to connect remotely with my MacBook Pro to this Hard Disk through the AFP protocol (afp://my IP), but suddenly I received a warning message "There was a problem connecting to the server".
I have read that Apple upgrade the securities of the AFP protocol but Im not sure about this and of course I dont know what is the solution.

I attach here an image of the message and I hope for any help
Thanks
Josef

I have to correct my self. I made a mistake with the settings of my Airport Extreme router and forgot to "share disk by Wan". It works very good.