My understanding is that the recovery img (TWRP) was replaced (? correct) during one of the OTA updates.
So I did reinstall the version 126.96.36.199 which was the only one working fine on my tablet due to calibration issue (I didn't try 188.8.131.52 yet)
Next, I did copy the OTA2.zip on a SD card and plugged it into the tablet.
I did boot on the recovery image (pressing both the volume + button and the power button followed by twice the volume - button and once the volume + button).
Once in TWRP, I did "Install" > "Using External "SD" > "OTA2.Zip"
After the installation, I did "Wipe Cache/dalvik"
And finally "Reboot System".
Once booted, I WAS ON Android 4.1.1 with Play Store available !!!
I LOVE YOUR FORUM !!!