Hi Nickstart, start checking if the problem is related with the kind of Disk and test on different brands, disk types.
Even if a recorder is supposed to work fine on both +R, -R etc. , often you find out, that due to error correction methor, a device worksd well on one or the other type.
Your DVD supports the following DVDs -R, -RW, -RAM, all -R disks are supported both on 3'' and 5''.
On +R it just writes regular DVD +R, DVD +RW and mini DVD +R are not listed in DVD specs, therefore are not supported on writing.
When your unit records DVD +R it changes the format to DVD-V, The usint does not support DVD+RV.
I assume it works better with -R
I often get troubles with many DVD low price brands, try testing some good ones like Verbatim, TDK, Sony , Philips etc.See also the manual here, at page 6 and 7
it also says: "Play may be impossible on some DVD-RW (DVD Video Recording format), +RW, CD-R or CD-RW discs due to the condition of the
Hope this had been helpful, test both a good brand DVD-R and a Good brand DVD+R.
If it still has problems when finalizing the CD, then it can be the usual lens problem, Or the DVD you are writing is too big in size and your player has problem on the final phase of DVD writing. If Data nearly takes all the 4.7 Gb allowed, there won't be enough space to finalize the DVD.