I have a DS loaded with the gba game Pokemon emerald my friend has a DS loaded with a DS game called Pokemon diamond when you try to trade you get a message wireless adapter not connected properly?

There is no way to trade between Emerald and Diamond, because they are for different systems. The closest thing is that if your friend has beaten the game then you can put your Emerald into his DS and put your Pokemon into his game. The only problem is that you can't trade Pokemon from Diamond to Emerald, only Emerald to Diamond.

however there is a way to get the Pokemon from a GBA cartridge to the DS cartridge. when you get in to the Pal Park supposedly if you have a GBA cartridge in the slot2 and a DS Pokemon game in slot1 the Pokemon from the GBA cartridge will "migrate" to the slot1 game.