Rocboxed Sansa Fuze V1 Transfer failed 2 times

[seamoon]

I have newly Rocboxed Sansa Fuze V1. So far in two times I've transferred totally 150 mp3s to it.  Today I tried to transfer about 30 mp3s, a minute later I get can't write error then when I click to drive icon I get drive is not ready error. I see write icon on mp3 player's screen is still active. I left it few minutes but still the same. Then I unplug it but usb icon on player stayed. I shut down it, connect to computer but again when I click to drive icon I get drive is not ready error. I unplug, shutdown and wait few minutes then try again, this time drive recognized but when I try transfer few successful mp3s  again get can't write error. Again unplug and tried again it transfer the rest of the mp3s.
After this happened, I tested it with 40 mp3s but get no error.

Is there a reason for this or is this known bug?

[Chronon]

You'll probably want to check the file system for errors.

I checked the bug reports and didn't find any obvious match.  Is this behavior reproducible?