Look for the previous logs in ImgBurn's Help menu. If it isn't there because you've uninstalled/re-installed ImgBurn then all we can say is read this -> http://forum.imgburn.com/index.php?showtopic=8000
Those logs only show you aborting a dual-layer burn right at the beginning and a single-layer burn. Please read this entirely -> http://forum.imgburn.com/index.php?showtopic=8000
Change the layerbreak back to Calculate Optimal in the program's settings and don't mess with it anymore. When you're burning X360 images load the .dvd file and it'll tell ImgBurn the correct layerbreak for that.
You can burn the DVD straight from each VIDEO_TS folder: use the 'Write files/folders to disc' option. If you still want to make an ISO image beforehand, use the 'Create image file from files/folders' option.
If you need more detailed instructions then have a look in the Guides section.
Those were all good burns and verified, so the discs should be fine. What may be happening is that the burn quality isn't good enough for your DVD player.
Here's what you can try:
update your burner's firmware;
try burning at 6x and 4x to see if turns out better;
try with Verbatim 2.4x DVD+R DL blanks if you can find them;
get a new burner that does good burns on those Verbatim 8x DVD+R DL blanks you have.
You'll probably need to re-author them in order to play both from the same disc. Have a look at Doom9's forum as I recall seeing something like that answered there.
DVD Flick comes with its own copy of ImgBurn, and it's an old version too. DVD Flick also saves the burn log in the same folder where you saved your project.
When you've uninstalled ImgBurn, it doesn't remove DVD Flick's ImgBurn copy.
Lots of questions for a brand new user...
Just the same way you think this forum is restrictive, one could say you're trying to lax our restrictions in order to make it easier to spam on our board. Just sayin'.
This is the real error and it means the burner wasn't able to write onto the media. And yeah, the write speed does play a big part in the burning process.