I've got a similar problem to skatermark420. I'm running Band Hero, it all loads (using USB Loader GX) and can play (using 223), microphones are detected etc. but the music store doesn't have any songs listed for me to purchase. I've updated my Wii Shop to v20 using the guide here with the latest IOS56 installed.
I've also tried deleting any saves on the wii system memory to make sure that wasn't causing the problem. I don't have any DLC content at all as I'm yet to download/purchase anything.
One thing is that i have a PAL region Wii and the game is NTSC, could this be my problem? I've tried forcing the game load to NTSC and that doesn't change it.