I recommend verifying that each of your dependent's last name and social security number is listed on your Tax Return exactly as it appears on your actual social security.  I suggest locating the actual social security card, not looking at a previous tax return or other documents to verify.

If a dependent has two last names or two middle names, that could be causing the issue.  

If there are two last names, use the "first" last name, then leave a space and include the last name.

If there are two middle names, use the "second" middle name as the last name, then leave a space and include the last name.  

Also be sure to include any suffix to the last name like Jr, Sr, III, etc.

Please comment below if you are unable to resolve the problem so I can assist you further.