Thanks for your effort. Sadly there is nothing there related to MMC except that you opened card door near the end of the log. Also the html quoting makes it quite hard to read :-) Maybe it could be better done when logged in from PC to tablet over ssh as root and running 'cat /proc/kmsg'. This keeps printing the log as it grows (until device hangs or crashes).

But don't bother if it sounds complex. It is possible there won't be anything interesting before the device crashes anyway.

As for the speed hack - it really doesn't work with every card. After all there must be some real reason why Nokia bothered to limit the MMC bus frequency to such low value (12Mhz). Perhaps the card must be more tolerant to signal noise or bad timing produced by 770 when running at higher speeds. My 2GB Kingston MMCmobile is rock solid at 48MHz. I am using it for more than year at such speed with whole system booted from it and swap file enabled and so far had no read/write error or crash that was provably caused by the card. But you are not first who reports such problems so there is not much you can do except trying different card.