You probably have a contact issue. Sounds like your 3rd DS Lite contact pins (for lack of a better description) are not as tight as your other 2.
I had the same issue on my sons DS and finally fixed it.
This is what I did.
1. Open the Acekard case very carefully, the clips look like they will break really easily.
2. I took an index card and cut it down to size, then folded it in half and put it underneath the PCB (component board). Then I put the Acekard case back together.
Now it seems to be working. At least for the past 30 minutes.
You may want to try something thinner. I worked my way up to a folded index card because thinner wedges did not work.
Good luck...
UPDATE -- Still have intermittant problems. Definately appears to be a contact issue, I am going to have to look into getting a replacement Acekard.