Diamond and Pearl help

I'm stuck in Mt. Coronet. There's this galactic grunt that's blocking my way and he says "I'm hopelessly lost! Please don't pay attention to a lowly grunt without any Pokemon!"
I have no idea what to do, I rescued the three legendaries from the Galactic HQ and I beat the 7th gym leader. Help?

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That link leads to the best place ,for videogame help.

^What he said^

I think you're supposed to go out from the East Side... PS, The new game out now is Pokemon Mystery Dungeon: Explorers of Time/Darkness.

EDIT: I ment in. Sorry ^^'