A few more details may be helpful here.
Does this also appear when reading files from internal storage?
There are a few possibilities coming to mind...
1) Something may have been broken in SD support by commits in the last ~3 weeks. There haven't been any other complaints though, AFAICS.
2) Your Fuze's internal storage may be on its way out. Reformatting may or may not help.
3) If only the µSD card is affected, this one may not be playing nice. What brand/model is it?
Concerning 2), try turning off scrobbling, which can make things a bit unresponsive at times due to the associated log file writes even when internal storage wear levelling is not running out of spare blocks.