GUIDE COPIED FROM HERE AS A POSSIBLE FIX, UNTESTED BY ME, REPORTS OF SUCCESS FROM OTHERS
1) Download http://www.multiupload.com/X65RBVD2MB
2) Unzip so you have just have "WW_epad-user-220.127.116.11.zip". Keep this zipped and copy to root of external SD.
3) Put another copy of the same file on your external SD card and name it "EP101_SDUPDATE.zip"
4) Put both files "EP101_SDUPDATE.zip" and "WW_epad-user-18.104.22.168.zip" on the root of your internal SD card.
5) Power down your TF
6) Power up into recovery - by pressing the power button and volume down button. Then press volume up when instructed by the screen.
7) You should now see the Android guy with some gears turning. This is good, actually this is GREAT! This will go on for a minute or so and then the device will reboot on its own. It will then go to the boot screen and you should see a bar showing you the progress of the update.
8) Once it has completed, install RazorClaw and root your device.
9) Do your happy dance because you are finally rooted like all the cool guys!
The above is "as is" and just a possible idea for those who want to try for root again - remember there are always risks involved when doing things like this - your choice, your tablet, your responsibility !
Root for B90 devices with .21 firmware - xda-developers