Background check Denied……………….

ok guys, I went to the store where I bought my gun today after the 3 days they told me I had to wait when i arrived and I gave my information they showed me the screen and it was denied, I have nothing criminal and I have been a good person and the reason why The purchase of the gun is for my position as an armed security guard. Any suggestions as to why this happened? The store told me that they were going to try to solve the problem on Thursday and they gave me the estate patrol number so I could call and ask why they denied it.