It's most likely the padding. Here's a way to get around padding for good.....
Before you burn your project, load it into VobBlanker.
Then tick Use Input Folder under the settings in the main GUI. Make sure the Smart Gaps is on in "More Settings" and save to registry (so you won't need to tick the box every time).
Now go Adjust sectors --> In Input Folder. This adds at least 32k padding where it needs it as tiny unreferenced files.
You'll never need padding again, and the padding that VobBlanker makes is very smart as it places the IFO and BUP on opposite sides of the disc, meaning that if the IFO has a read error, the BUP has a real good chance of being read.
Once this is done, ImgBurn will never need to pad again, since there will always be at least 32k gaps (subject to dual layer burns needing to move around a bit to honour the rules of setting the layer break).
By the way: EXTRA_TS is not a valid DVD folder name. If you want photos, JACKET_P is a folder that can house appropriately sized pix (google the specs of the pix). Or just have a folder called "DVD ROM files" or something.
Regards