We enable my site with all the feature having a task list in the quick launch,we created a new tasks in the site,when we tried to refresh the tasks i was not refreshing it was showing an error as shown in the screen shot.
Step 2: Now check the service is in started mode or not,Navigate to Central Admin->Application Management ->Manage services on server.check the status.
In my case it was not started.click on start.
Also verify the Service having permissions with "Application Pool" Service account with Full Control.
In my case i given the application pool Service account with full control to "Work Management Service Application"
Finally we verified at tasks,it was refreshing with out any issues.