Hi,
There are no updates for custom roms
and you cannot update custom roms using pc companion.
you can only update a custom rom if there is a new custom rom posted by the developer... e.g racht's Floyo-0.15--> upgraded to --> Floyo-0.20
If you want to go back to the official SONY Ericsson's 2.1.1
then...
you can use xRecovery to flash your original rom backup
OR
switch off your phone
launch pc companion on your PC
plug in your USB cable to your phone
hold the back button and plug in your USB to your PC
the repair process should start...
cheers