Why was I denied to purchase a handgun in Feb 2014 when I legally purchased one 3 months earlier? I live in Kentucky

I passed the first federal firearm background check but the second one denied me. In 2007 I was charged with a class D felony and accepted the pretrial diversion program which I successfully completed. My background says that the charge was dismissed-diverted. According to the paperwork the judge signed, if I complete the diversion program I do not have to acknowledge the occurrence of the crime. How does the FBI approve my firearm application the first time then deny it the second time. I've started the NICS appeal process and so far the only letter they've sent me says I was denied due to being a felon. I wasn't CONVICTED of the crime. I was CHARGED with it, completed diversion, and now it shows up dismissed-diverted so why am I denied to purchase a firearm now after legally buying one.