A DVD+R have two types, the physical (disc-type) is DVD+R, you can´t change it. The other type (book-type) is normally DVD+R, but with some writers you can change it to DVD-ROM. Some drives/players now think it´s a pressed DVD-ROM and maybe the player play it, when it won´t play the disc with the booktype DVD+R
How you can set it? It depends on what writer do you use. With Liteon you can set it (before burning) with their booktype-utility, with some other writers like Benq, newer LG´s you can choose it in Nero in the recorder-properties.
Benq DW 1640, LG GH-20N, Pioneer BDR-208
Crucial M4, Sandisk SSD, Plextor M5S, Sandisk Ultra Plus, OCZ Petrol 256GB