You are using SharePoint 2013, you have deployed My Sites. You or your users have tasks assigned. But when you or your users visit [···]

While you are opening Newsfeed and clicking on the following items you will face the below error/warning.

You have SharePoint 2010 or 2013 environment. You have also deployed My Sites and your users have been consuming the My Site Feature. You [···]

You have deployed SharePoint 2013 and the MySite functionality has been deployed. When you visit your Mysite and switch to the My Tasks screen, [···]

You have deployed SharePoint 2013 and the MySite functionality has been deployed. When you visit your mysite and switch to the My Tasks screen [···]