Database and display issue upgrading from 521 to 524

Hi,
I "maydayed" Roel for an issue described in problems topics.
We together found the solution.
Description :
After upgrade, display of many php errors, first line (name, date, login) not visible when logged in.
Impossible to logout ... and impossible to make change in settings as it sends me an "invalid request" answer.
Errors linked to settings table according to Roel.
As I have another 524 but brand new on the server, made a comparison between 521 and 524 settings table.
It shows differences and more fields in 524.
Made a copy of liable settings table from brand new to my imported datas, scratching imported settings table.
All ok, no more issue ! Just some data to change, minor problem.

Conclusion :
Roel thinks an error occured in the upgrade procedure which is supposed to correct the structure to new standard.
No key for this trouble as it seems nobody else encountered, just a solution ..
Could be  a tricky external cause, nobody knows.

I write this here after Roel asked me to, in case anybody encounters the issue.