It seems there are many webmasters complaining that the "Links To Your Site" section within Google Webmaster Tools is showing the error message, "No data available."
I personally do not get this and I believe there were no changes to the number of links shown in my report but there are dozens of complaints in the Google Webmaster Help forums with complaints about the issue.
Some even posted screen shots, here is a screen shot that I cropped a bit:
Google has not yet responded to the complaints in the forums.
Google Webmaster Tools is known to have reporting issues from time to time, so I would not worry if you are affected.