This from G&T explains it well:
UPDATE Oct 1st, 2010:
A new Android 2.2-0831 CMO version firmware has been released by Witstech. This firmware works for the newest (as of now) A81E tablets shipping that have slightly different hardware than A81E tablets shipped earlier this year. If you have tried flashing one of our other firmware & have issues with a white/half-working display screen, then download & flash this newer 2.2-0831 CMO version firmware to fix your issue.
'slightly different hardware' is an interesting phrase...
*** NOTE [EDIT: October / 01/ 2010] ***: Witstech has been shipping slightly different A81E tablets lately, & it's been brought to our attention that these newer versions will not be able to flash the other A81E firmware versions we currently host. We are contacting Witstech to find out how members may be able to determine if an A81E is of the older hardware or newer hardware version before they make a mistake & flash an incompatible version firmware to their A81E.
If you have already flashed your new A81E tablet, & you experience an issue where some/half the screen is white & the rest of the screen may look distorted, then you most likely have one of these newer A81E tablets, & therefore you should download & flash the "CMO" version firmware we are now hosting. So far this CMO version is the only one we host which is compatible with the newer A81E tablet's hardware.
Below firmware is the newer CMO version for the latest A81E tablets being shipped:
Android 2.2-0831 CMO Firmware (Improved Bluetooth, Market working, GPS, USB, Languages)
If you have had your A81e for a while, below is the firmware for most, now older, A81E tablets:
Android 2.2-0831 Firmware (Improved Bluetooth, Market working, GPS, USB, Languages)
Android 2.2-0823 Firmware (Bluetooth, Market working, GPS, *Languages)
*Seems the Languages included from the last 2.2-0818 update are now missing with this update.
Android 2.2-0818 Firmware (Market working, GPS, *New Languages)
*Languages include: Chinese, English, German, Italian, & Russian.
Android 2.2-0809 Firmware (Market working, GPS)
Android 2.2-0802 Firmware