Please help! Importing comments error!

Hello,
I have followed the installation guideline to setup Ultimate Facebook.

It posted to my fanpage just fine.
But it would not import the comments from the post it posted.

When I clicked on "Import comments now" link. Nothing.

And the error log showed:

Date User Area Type Info
April 6, 2013 2:48 pm Unknown get_feed_for exception An unknown error has occurred.

And my server error log did not record anything.

I have been trying for two days to get it to work.

What should I do? Please help.

Anne