You are going to dislike your Samsung then as it is not an error with ImgBurn. Nero does it as well for people.
Use DVD-R as I never saw it happen on any of my Samsung writers with DVD-R
After reading many posts about this issue I've come to the same conclusion as dontasciime suggests.
Until recently I had no problems burning DVD+R (Verbatim) on Samsung ODD, at home I use SH-S182M and at work SH-S203P.
Whenever I attempted to burn on DVD+R (no matter whether single files or prepared ISO image) the Finalization of disc failed on me
I 08:55:11 ImgBurn Version 126.96.36.199 started!I 08:55:11 Microsoft Windows XP Professional (5.1, Build 2600 : Service Pack 2) I 08:55:11 Total Physical Memory: 3