Plugins Google+1 and TweetThis are no longer supported and are replaced by the new plugin Social Buttons. The idea is to have all your social media buttons merged into a single plugin. Social Buttons currently manages 5 social networks: Google+, Twitter, Facebook, Pinterest and Tumblr.
Plugins Google+1 and TweetThis are not available on Piwigo 2.5. For a faster upgrade of your photo gallery to Piwigo 2.5, deactivate these plugins. Let’s also say that FacebookPlug is not compatible yet with Piwigo 2.5, so if you’re only interested in the “like” button feature, replace it with Social Buttons too.