update variable from 7.1 to 7.2 : got error message "The form has become outdated" Got D7 multilingual configuration with many modules, from which i18n...

Trying to update variable from 7.1 to 7.2 version, following http://drupal.org/node/1660798 #1 tutorial (I also tried other methods explained in other nodes like http://drupal.org/node/1670274 ).

After clearing cache (twice !), replacing old i18n and variable folders with the new ones, I try to run update.php. Nothing happens, I mean reloading same page... I try then to put website into maintenance mode.

After submitting maintenance mode form, got error message "The form has become outdated. Copy any unsaved work in the form below and then reload this page."
So I tried to put first into maintenance mode, before replacing folders. But then back to the same story : update.php reloads its page so I have to check again if I'm still into maintenance mode : BUT I'm not anymore...!

I guess what may happen is that changing variable folder generates the following mistake : Drupal doesn't read correctly its database variables, so doesn't see any more it is into maintenance mode ? 

So who from the egg or hen comes first ? How could I manage that and stop eating aspirin ? Thanks a lot for sharing experience
So to answer the question :

for people who don't manage to update simultaneously variable and i18n to get variable 2.1 &amp; i18n 1.7 :

even if unusual, you have to update first from your current version (i.e i18n 1.4  and variable 1.1 ) to i18n 1.5 and variable 1.2, only after that you'll be able to update to variable 2.1 and i18n 1.7 versions.

Always following same steps :


clear cache
replace modules folders with the new version
run update.php