I never heard of a Ibox DVD writer, but perhaps they're more prevalent in Europe.
It appears that youâ€™ve updated your firmware to the latest using the link you indicated. From that link I saw the unit does have bitsetting capabilities.
You can try using the bitsetting utility that appears on the same download page as the firmware update. Also download the bitsetting users guide that has instructions. What bitsetting does is changes a DVD+ disc to a DVD-Rom disk, this is the format used on original store bought DVDâ€™s.
In simple terms, it fools the DVD player into thinking itâ€™s an original, thus making it more compatible with most standalone DVD players. YOU MUST USE DVD+ MEDIA ONLY, bitsetting does not work with DVD- media. Use the utility to change a new DVD+ before you burn the movie, wonâ€™t work after it is burned. You must do this for each disk you plan to burn. The firmware on my Liteon burner is customized and any DVD+ I put in will always burn as DVD-Rom. I have loaned my disks to over a dozen people with all kinds of players and never had one complaint about the disk not working properly.
The Ritek media is not the best, but it is very good media and really should not be causing the problems you describe unless you got a bad lot. You didnâ€™t mention if it was + or -.
Unsure if these media types are readily available in the UK, but try buying a small pack of Maxell or FujiFilm (made in Japan only, NOT TAIWAN) of DVD+ and use the bitsetting utility to see if you can get a successful burn. In my opinion Taiyo Yuden is the best media available but sometimes hard to find at a reasonable cost, the FujiFilm made in Japan are usually Taiyo Yuden.
To verify who the manufacturer is download the free DVDInfopro from dvdinfopro.com.
Insert the media, click on the media icon , top far left, and it will tell you the manufacturer.
Your Riteks should be indicating RicohJPN002.
I donâ€™t use printed labels myself or print directly on a DVD but from what Iâ€™ve read it should not cause any problems. You can easily verify this by burning the DVD and not printing on it, if it skips and freezes you can rule out the printing caused the problem.