PANICKED! Arrest from almost 20yrs. ago surfaced on background check!

HELP!!! I need any feedback from anyone who has had this problem!
I have worked as an LPN for the past 7 years and recently graduated with my RN degree. After all the stress and nail biting.. my authorization to sit for boards came and I scheduled for mid July. Today, I recieved a letter from the state BON that I had an arrest/conviction that showed up from 2/1992! I was in total shock and could have literally vomited right there on the floor! This was a stupid mistake I made in my youth that had something to do with tampering with a mailbox for which a pre-trial diversion was made, restitution paid, probation completed and then expunged from my record. I assumed the arrest record would also be expunged and I could go on with life, however, with the fingerprinting now being required, I have to deal with this mess.. almost 20yrs later! What's worse is that they want me to send a letter and provide all this documentation and I can't even remember who the attorney was, much less who my probation officer was.

Has anyone had to deal with the TN BON in regards to something like this? What was it like? I plan to call the BON after the holiday and try to reach someone at the court to see what kind of documentation I can get to send in, but I am more stressed now than I was for my final nursing exam!!!!

Please! Any feedback will be greatly appreciated!

Thanks!!!