You must have seen this error in "Review problems and solutions" section of Central Administration of SharePoint Server 2010 so as I. So just thought of writing about the same and its resolution.
Activity Feed lets users add feeds of events to their My Sites. Feeds might give information about activities of their Colleagues, such as updates to profile properties and creation of social tags and notes. Activity Feed does not enable tracking of activities that a user does not have permissions to see.
Activity Feed is off by default in a User Profile Service Application.
To turn on this feature, a member of the Farm Administrators group must configure the User Profile service Activity Feed timer job.
- On the Central Administration Web site, on the Quick Launch, click Monitoring.
- In the Timer Jobs section, click Review job definitions.
- Click User Profile Service - Activity Feed Job in the list of timer jobs.
- On the Edit Timer Job page, click Enable.
And finally we see that the problem is solved
Users choose their Colleagues for their My Site by selecting names of other users and setting them as Colleagues. When a user is selected as a Colleague, a notification e-mail message is sent to the new Colleague.