The error you are describing, happens on Title Update 5. You must be on Title Update 4 to play customs. Also must be a physical disc with EA logo on the disc. It cannot have the madcatz logo (4 red, diagonal scratches over a black square). That disc will not work.
You are about to leave Rhythm Gaming World and access the external songs DB. While no song or file sold for commercially available videogames is hosted there and only fan generated content is allowed, Rhythm Gaming World has no direct control over the database and no files are hosted here. Alright, we had to made you aware of this, now you can visit the database!
