I have one SD card that crashes my SJ.  That's one out of 10 or so.  It started a week ago and it would crash on one jam track that I deleted but the SJ said was still on the card.  Same thing-- a pop then re-boot.  I filled up the card with tracks and now when I plug it into the jam it just immediately pops and reboots and it wont show any of the tracks I've put on there.  I've had the amp for over a year and it's been great.  My other SD cards work fine (so far) except for one particular card.  All of the cards are the same--Sandisk 2 GB.  I just wonder if it is a defective card or is this problem going to get worse?  And this particular card that crashes my SJ was working fine with playing along and loading/deleting backing tracks for about 2 months until this past week when it has popped and re-booted 4 times and now I will not put it back in because I don't like that sound.  And again, I've checked my other 10 or so full SD cards and they seem to work just fine.  I just hope it's an isolated incident and not something going wrong.