When we call in on a 4473, we get either Approved ( equals the FBI Proceed ), Conditional No ( Delayed ), Denied. The approved NICS Number is XXXXXXXA where X is a number. Conditional No is XXXXXXXXCN. Denied is XXXXXXXXD I believe as we have no Denieds yet. A CN means in 3 working days, the FDLE will give an approval or denial. If no response from them after 3 days, it is up to the FFL if they wish to transfer the gun. A Denied means the person will have to file an appeal with the NICS number that was denied to the FBI. ATF provides a card for giving to a customer who gets turned down. It is also is covered in ATF Publication 5300.4 page 226 and 227. To do the appeal, you also have to have fingerprints taken in most cases and submitted. And it all has to be done in writing or e-mail/fax. They will not discuss it on the phone. They have 5 working days to provide the reason for your denial after they get the appeal. Then it is up to the buyer to provide corrected info to them for reconsideration.
Good luck to your friend as it could be something as simple as two people with the same name in the same county. A common CN cause is not giving a SS number and two people sharing a name. When I bought some property in Orange County, FL, I had to file a Not Same Person affidavit due to several bad apples with the same name.