Error 500 in 'Recent activity"

1)Log in
2)Add the post(255 characters)to any topic
3)Go to the page with list of branches (http://deploy.jtalks.org/jcommune/sections)
4)Click on "Recent activity"

Expected result: You should see the message you've just posted in the list of Recent activity
Actual result: Error 500: Server encountered an internal error while processing the request. Please check if the URL is valid and try again.