textStatus: "error " errorThrown:"Internal Server Error " jqXHR: " "

All files upgraded. Now upgrading database...
[Ajax / Server Error for action upgradeDb] textStatus: "error " errorThrown:"Internal Server Error " jqXHR: " "

The error happens when trying to upgrade prestashop version. Do you have the same error message ?

When tried to rollback the changes. My prestashop back office seems to work OK but not OK for my front office I get 404s on all my pages except the main landing page.

Database restoration file 000027 done. 32 file(s) left...
[Ajax / Server Error for action restoreDb] textStatus: "error " errorThrown:" " jqXHR: " "
 This it is a permissions issue, related to some Apache rules.

The solutions is trying to increased the timeouts (and a few other limits) in the ini files and the problem went away - and the 1-click upgrade worked flawlessly.

 First, there are three ini files, so to be safe I made the same changes in all three files. Those files are:
  1. php.ini
  2. php5.ini
  3. .user.ini
All are in the HTML root (not the prestashop folder). You likely only need to do this in one place, but I did not want to keep experimenting and don't have the knowledge to know which one to use, so I used all three and made them match.  :)  These are the lines I either updated or added:
  • upload_max_filesize = 640M
  • post_max_size = 640M
  • max_file_uploads = 200
  • memory_limit = 320M
  • max_input_vars = 3000
  • max_input_time = 600
  • max_execution_time = 600
  • set_time_limit = 600
It was likely one of the time limit settings, but I increased the size limits as well so I wouldn't have to keep experimenting. Feel free to chime in if any of these are a bad idea. Note that I previously had the timeouts at 300 (5 minutes) and changed them to 600 (10 minutes).