Having problems with File Sharing

I want to use File sharing to backup my macbook through my external hard drive on my iMac. Put when I turn on file sharing, I see my macbook in the finder's sidebar but it does not connect.

What gives?

Are you sure that you have File Sharing enabled on the iMac? Check the Sharing section in System Preferences and make sure that File Sharing is checked. Also, add the external hard drive to the list of shared folders there.