Notification of CAC ineligible during Deployment.

Okay…I just need some others perspective and any advice.
I have been deployed in Iraq for the past 6 months as a contractor (Firefighter)…I received my NACi and have been working for the past 6 months. Today I received an email from the USARCENT stating that I have been deemed ineligible for a CAC because of something on my record 20 years ago.
I do not require a CAC for my job however I was told by my HR that I must remain CAC eligible to keep my job…
When I was 18 and in the USMC I went out partying with some other young Marines and failed a drug test. I have received a DUI a fee years back as well but the charges were dropped and the record expunged.
I spoke to a military attorney today that thinks he could fight it…but wants $5k to start the process.
Anyone have any experience with this?