What can I do if my Security Clearence Denied?

I am, or at least was in DEP for the Air Force reserve since October and now two week before I was going to ship I was told my security clearence was denied( I didn't lie nor did anything wrong) so I was told all air force jobs requier a clearence, is that true? Should I try the air guard next? My recruiter said I can go to another service and try for a job the doesn't requier a clearence but I really want to join the air force, what should I do?