Hmm, sounds like a sensitivity problem with the screen. It could be a hardware fault but then again it appears to work during the initial setup.
Read this thread here (viewtopic.php?f=85&t=65073
) particularly the second post:
You need to reboot into recovery (restart and then hold vol down) and perform a screen calibration. My device was doing that when I was out in extreme cold temperatures. After a calibration (not from within Android, do the one in recovery), your problem should be fixed.
Do you have a screen protector stuck on your tablet?
Are you holding it by the corner (bottom right) and letting your thumb accidently touch the screen?
P.S. Assuming that you've got the Honeycomb version of the 70b then you should be using firmware version 3.2.81 from here: http://update.archos.com/9/gen8v2avx9/g ... os_it3.aos