Google added the ability to verify and merge your Google+ local pages with social pages a week or so ago. Many have already transitioned the pages over but many have yet to do it.
Those trying to do it today may not be able to because the feature is 'erroring' out with a 500 error response code.
Jade, the Google+ Local community manager said in a Google Places Help thread that they are aware of the issue. She wrote:
Seeing reports of users getting 500 errors when attempting to verify their social local Google+ page. The team's aware and working on it. I'll post back on this thread with updates.
You can help by: - Sending feedback from your profile or page. Either from the gray Send feedback text on the bottom of the right column on your page, or, from the gear icon. - Posting links to the pages you are trying to verify here.
Thanks for your patience!
So sit tight, Google will hopefully fix it soon.
Forum discussion at Google Places Help.