Pokemon Ds keeps freezing while in the underground?

Hi, I've recentlybought pokemon platinum for ds and there seems to be no problems exept when I enter the under ground ( which uses an internet connection ) However every time I enter the underground the game always freezes within 10 seconds of entering the place. I've used the other online functions such as the plaza etc. and they all seem to work fine, yet the underground never works for me. I've also heard of a fewpeople who have the same problem, yet no-one knows why. I did purchase this game second-hand yet since allthe other online functions work besides this one, i doubt it has anything to do with it. It also seems thatthe icon that shows the signal strength of the distance between you and your connection seems to be always red even though my connection and wifi areon and working fine.

Thanks for your help :P

Check to make sure your copy isn't a bootleg (compare pics on ebay or something). Bootlegs freeze all the time.