Burning at the slowest speed is not the best policy with modern burners and the 16x media we have nowadays. With Memorex, not knowing the manufacturer id code, I'd choose half the rated speed...so if you are using 16x burn at 8x. 8x reduce to 4x. These are general guidelines only.
I would burn with ImgBurn. It is a free burning program. www.imgburn.com It has the added benefit that it can bitset +R disks for you. (bitsetting isn't done for -R disks).
To set booktype or bitset, open ImgBurn and make sure your burner is the selected drive. Click on Tools-->Drive-->Change Booktype. This will open a window with a list of manufacturers. Click on LG.
In the drop down box across from Change For: select DVD +R Media.
Across from the New Setting select DVD-ROM. Click on Change, then click OK.
I would also seriously consider different media. Try some 16x Verbatim.
Let us know if any of this helps.
Edit: Here are the guides for using ImgBurn: http://forum.imgburn.com/index.php?showforum=4