There are technical differences between the two I think, as well as a small difference in size, but these days most players support both formats. However some players are known to be a bit picky, hence the need for bitsetting - changing the booktype of the disc to DVD-ROM, which is the booktype of original, pressed DVDs.
Has your Panny ever played any other burned DVD+R successully? If not then the simplest option would probably to reburn to DVD-R, and just stick with that format for use on that player. As it looks like media quality might not be the culprit, if your Panny plays Melody DVD-R OK.
Our of curiosity, what's it say in the manual? Usually it says what discs are supported under the "specifications" section.