Not all DVD players are equal. Some can play just about anything you stick in it. Others aren't so good. Some can do -R, some can do +R, some can do both but maybe not equally.
Also, not all DVD media is equal. Some media is better than others. Memorex is usually not listed in the "top media" lists.
A couple things you can try:
1. Try -r instead of +r
2. Try a different brand of media. TY is generally touted as the best. I've had good success with Verbatim.
Edward Troxel