Format error is due to hacked memory.
Once the real memory fills up everything else is just indexed with no actual data behind it. As you add and remove different files the index becomes really messed up until nothing will work on the player and thus you are formatting to fix it.
A better idea is to remove the hack by following the instructions I posted here....
PROBLEM TO REMOVE AN MP4 hacking
First you'll need to confirm the real capacity. I personally just 400MB movie files one by one and when I get to one that will not play I know I have overstepped the true capacity. I then use Check Disk as outlines in the linked post to recreate the boot info.
I find all the other guides are outdated in regards to the new players coming out of China.
Check Disk has worked for all the Touch Screens I buy as well as the Nano clones.