Okay guys - I answer this by my own...
The solution is really easy - simply use LG tools to flash that device!
I have a link how it works for LG P500 - but this also works for the E720!
First read this and get the flasher software:
LG P500 Firmware Download - LG Cell Phones Blog
I just downgraded 2.2.1 to 2.2. using this method.
The flash-programmer tool is KDZ_FW_UPD. I booted my LG to the 3e-menu when starting running the upgrade because when direcly connecting my pc to emergency-mode the USB-Drivers hang. Maybe this is local problem here - maybe not. It works better from the 3e-menu (that android with the yellow exclamation mark).
You also might try directly from emergency (press vol+ vol- and power - keep the 3 buttons press down and have USB PLUGGED IN).
the kdz firmware itself is from LG site:
The Android 2.2 version (rootable)
The new Android 2.2.1 (not rootable yet)
So LIFE IS GOOD for me, again and I AM (nor google neither LG) the only root and admin on my devices :-)
- ehm.. yeah - this is GERMAN version ADEUBK - you might download different!
AITABK for example for ITALIAN.
The available versions you find with this link:
and above all: have back the power! be ROOT