While attempting to add another developer to my Facebook Application Settings panel after I tried to save his name, I got the following error:
Only verified developers can be added as listed developers of this application.”
A Google search brings this blog post which says here http://developers.facebook.com/blog/post/386 that
“Starting this week, we are requiring every developer to verify his or her Facebook account to create new applications. This is the same quick process that users go through when they want to do things like upload large videos.”
“You can verify your account by either confirming your mobile phone or adding a credit card to your account. Facebook will not charge your credit card if you add it to your account.”
Verifying mobile number did not resolve it and I suggested him to first add the application where I was adding him as developer and that worked for me. After he joined that Facebook app as a user, I could add him in the developers list.