D2+ white screen on boot

[mammoth]

I'm running rockbox from an SD card, with Cowon fw 3.13, on a D2+. I have successfully booted and used rockbox once (on the first try with this card), but on subsequent boots I get the rockbox splash and then a blank white screen. No error messages. No buttons or touch areas do anything to the screen. I can only press the reset button.

I have searched for any other reports of this problem and have found none. Does anyone know of a solution? Thanks in advance.