Does
PR 5739 fix the issue with Rock Band DLC? It was recently tested with DLC and should be working.
No dice. The system menu gives me the same "The Data may not have been moved/copied" error; whereas Rock Band 3 now tells me that there is not enough room on the Wii's system storage to use DLC (which is different, so that's progress I guess.... not sure as to how that's relevant to moving data OFF the internal storage though)
If you enable logging at the info level for IOS and IOS_ES, we should be able to see what went wrong.