I know what you're referring to--the dark green CDRs. Today they are all silver-like. In fact I got a brand new LiteOn burner and it doesn't burn well at all to these old CDRs!
I would suspect they are no longer being manufactured since all new drives on the market are optimized for the newer dyes. Also I understand that dye ages over time and old blank media deteriorates and gets harder to burn. Don't know if that is true--since my old green CDRs still burn fine on my older burner.
Maybe if you contact the manufacturer they may have some kind of firmware update for your unit or may recommend some media that works.
You may be able to find some old stock being sold on eBay. I have some myself which I try to use but now that I got a new DVD writer I don't know if I will...