If you power your BBB using USB power you’ve probably found the board will power off unexpectedly and/or not boot from the SD. This change allows > 500mA through the mini-USB port.

Edit the uEnv.txt (located in /boot) and add this: i2c mw 0x24 1 0x3e

Your uEnv.txt fill will end up looking something like this:

uenvcmd=run findfdt; if test $board_name = A335BNLT; then i2c mw 0x24 1 0x3e; setenv mmcde…

To give credit where its due I found the fix here: http://archlinuxarm.org/forum/viewtopic.php?f=28&t=5486#p32325