Hi Support! Thanks for supporting. I was trying to finally upgrade our Mediawiki 1.15 to 1.21, but did not succeed. Of course, I backed up everything before, so I could now restore the 1.15 to working function. Still, I am not sure why it failed. I noticed several different error messages and will supply them later. For now, I would like to clarify that I indeed use the correct order of actions:
1) Copy 1.21 files into 1.15 folder 2) Run /mw-config/index.php to upgrade database I was not even able to complete this step.
I also tried another order, also without success 1) Create new folder for 1.21 files 2) Ask 1.21 to access 1.15 database 3) Run /mw-config/index.php to upgrade database