Same issue for me - I would gfet kicked from the store for "lack of memory" like the others here, but generally when trying to load the track preview. Was able to DL 4 RS tracks yesterday w/ no problems.
Will try the online Quickplay trick. At worst, it sounds like deleting the save file works. Unlike RB2 & it's near year of collected save data, I can live with losing my Beatles data - just a good reason to replay the Story mode.
BTW, the reason this save data can't be moved is the same reason most online-equipped Wii titles do not allow it. Portions of your save data are tied to your online & Wii Shop accounts. In order to keep folks from doing things like swapping DLC btwn consoles - and according to Nintendo to "preserve the integrity of the Wii's online service" - such data is tied to your Wii. Mario Kart & Smash Bros are other examples of online games that must retain save data internally.
Some online games - in particular GH5/BandHero & a few other recent titles - DO allow you to copy your save data to SD card. However, when you do copy it, you are informed on screen that the data is only playable on YOUR Wii. ANd in these cases, you can only COPY data, not MOVE it.