We're talking about form I-539? The question, "Have you, or any other person included on this application, ever been arrested or convicted of any criminal offense since last entering the United States?"

An ACD (Adjournment in Contemplation of Dismissal), if successfully completed, results in dismissal of a charge (it's not a conviction) but it doesn't make the arrest go away. The USCIS appears to believe that you lied about your arrest record - and a willful lie in pursuit of a visa can result in your permanent exclusion from the United States. I suggest working with an immigration lawyer.