Hello Skubbz and welcome to the forum.
What brand are these DVD+R DL discs? Do note that many writers have problems with writing to DVD+R DL discs other than those made by Verbatim. This happens most often with Ritek branded discs, usually those that are rated as 2.4x, or have no speed rating printed on them. Many companies get these same discs and have them rebranded, for the reason that they are cheap.