How do I put a 2 disc set of a movie onto one dual layer?

So i have discs 1 and 2 of wyatt earp and I made an iso from dvd shrink but when I tried to burn it with imgburn I got the this message:

Optimal L1 Data Zone Start LBA: None found! (VTS_02)

This image has not been mastered correctly for burning onto a double layer (OTP PATH) disc.

None of the cells meet the ‘DVD-Video specification’ criteria for a potential layer break position.

What do I need to do?

Have you reauthored the titles on the discs or have you just combined the two ISOs?

If you’ve already reauthored them then check out the guide in my signature for help in choosing the best layer break position.

If you’ve just combined the two ISOs then you’ll need to reauthor in DVDShrink.

Check out this thread for a quick guide on combining two discs.