Teac dv-w518gm

Hello All,
Thank You for usefull information placed on this forum.
I’d like to get Your assistance about following issue.
I purchased my Teac-DV-W518GM DVD recorder (Revision ZT14) more than one year ago and till now I haven’t any problem with it.But after I bought Verbatim 8.5 Gbyte dual layer DVD disk my recorder cannot recognize it . After reprograming of firmware to LiteOne LH-18A1P lastest GL0J revision, the problem persists. I know , that my recorder able to burn dual layer DVD regardless on it’s +/- formats.
I have no problem to born regular Verbatim DVD.
Please advise.:bow: