Redmine

After upgrading my local MariaDB version i can't run redmine anymore; after checking the log i found out this:

[ 2016-10-13 21:33:36.2518 2319/7f763b7fe700 age/Cor/Con/CheckoutSession.cpp:285 ]: [Client 2-3] Cannot checkout session because a spawning error occurred. The identifier of the error is 4f8ea207. Please see earlier logs for details about the error.
App 6817 stdout: 
App 6817 stdout: 
[ 2016-10-13 22:09:26.5580 2319/7f76401f1700 age/Cor/App/Implementation.cpp:304 ]: Could not spawn process for application /var/...../bugs: An error occurred while starting up the preloader.
  Error ID: 3ada3e39
  Error details saved to: /tmp/passenger-error-KQidBu.html
  Message from application: There was an error while trying to load the gem 'mysql2'. (Bundler::GemRequireError)
  /usr/local/share/gems/gems/bundler-1.11.2/lib/bundler/runtime.rb:80:in `rescue in block (2 levels) in require'
  /usr/local/share/gems/gems/bundler-1.11.2/lib/bundler/runtime.rb:76:in `block (2 levels) in require'
  /usr/local/share/gems/gems/bundler-1.11.2/lib/bundler/runtime.rb:72:in `each'
  /usr/local/share/gems/gems/bundler-1.11.2/lib/bundler/runtime.rb:72:in `block in require'
  /usr/local/share/gems/gems/bundler-1.11.2/lib/bundler/runtime.rb:61:in `each'
  /usr/local/share/gems/gems/bundler-1.11.2/lib/bundler/runtime.rb:61:in `require'
  /usr/local/share/gems/gems/bundler-1.11.2/lib/bundler.rb:99:in `require'
  /var/www/vhosts/f.....bugs/config/application.rb:5:in `<top (required)>'
  /var/www/vhosts/.....bugs/config/environment.rb:2:in `require'
  /var/www/vhosts/.....bugs/config/environment.rb:2:in `<top (required)>'
  config.ru:3:in `require'
  config.ru:3:in `block in <main>'
  /usr/share/gems/gems/rack-1.6.4/lib/rack/builder.rb:55:in `instance_eval'
  /usr/share/gems/gems/rack-1.6.4/lib/rack/builder.rb:55:in `initialize'
  config.ru:1:in `new'
  config.ru:1:in `<main>'
  /usr/share/passenger/helper-scripts/rack-preloader.rb:110:in `eval'
  /usr/share/passenger/helper-scripts/rack-preloader.rb:110:in `preload_app'
  /usr/share/passenger/helper-scripts/rack-preloader.rb:156:in `<module:App>'
  /usr/share/passenger/helper-scripts/rack-preloader.rb:30:in `<module:PhusionPassenger>'
  /usr/share/passenger/helper-scripts/rack-preloader.rb:29:in `<main>'

[ 2016-10-13 22:09:26.5675 2319/7f763affd700 age/Cor/Con/CheckoutSession.cpp:285 ]: [Client 3-3] Cannot checkout session because a spawning error occurred. The identifier of the error is 3ada3e39. Please see earlier logs for details about the error.