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.
Step 3:
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.