I have came across this situation with the same model, however it looks the firmware being put on must be of the same type already loaded. Could you check what firmware came with your DVD recorder? This should be located on a sticker to the right of the DVD recorder (at least the drive I seen).
On the recorder I updated, I tried putting LNMPE018.DA5 on a CD-RW written in ISO mode with Nero, however I got the same symptom as yourself in which the DVD recorder reported ‘Data Disc’. I spent over an hour trying different recording applications (including the Windows own disc writing utility) as well as different extensions (DA0, DA1 . . . DA9), etc. Then I checked the sticker to see that it had ‘LNMRG018’, which looked quite different. So, out of curiosity I downloaded the German firmware and noticed it was in sequence with what the drive had loaded - ‘LNMRG019.DA3’
As the menu’s language and country regions list both English / Ireland and German / Germany respectively, I figured I would be able to change the settings back to English and Ireland if everything appeared in German, so I went ahead and wrote the ‘LNMRG019.DA3’ file to CD-RW using Nero as before and when I popped in the disc, it asked if I wanted to update the firmware. I selected ‘OK’ and the process began. During the update, the tray ejects and when it finishes it asks the user to repower the system. Once I done this (put the unit in standby and powered it back up), the menus came up in German.
Finally, I selected English for all the language options, set the country to ‘Eire’ (Ireland) and retuned in the channels (both UHF and VHF) without any issue.