I am all agreed with Ziatron!
I personally still work in iMovie'11.
iMovie '11 (v9) : shares and/or exports to m4v-file (iTunes) or QT (I never use that)
iMovie '13/14 (v10) : shares to iTunes etc. but also saved as a file (it will be mp4) (I personally do not work in that program!)
I use a purchased converter 'Wondershare Videoconverter Ultimate 1.6.2' (Yes that's an older version, I never use the new upgrade!)
I burn a long time iDvds. But sometime they give problems!!
But I always say... NEVER GIVE UP! and I usually convert my files and try again and win.
Today... I also got problems:
First time I wanted to burn a dvd I got an codec-error! (Like you Brenda!)
So I tried to convert the files and tried again... same error.
Then I thought, if I convert again but different...:
So I converted to Mp4 files of 1280x720 at H.264 Normal codec, instead of HD.
... and yes... it worked: dvd burned successfully in 33 minutes. (Highest Q, 75 minutes disc)
Another matter is: keep your workflow correct and keep your unwritten dvd-discs clean. I even once purchased an inferior Sony-spindel!! (but that'll be 'disc-errors').
I know it's all frustrating matter for you Brenda, if things don't work well or even systems do not compare right like Apple use to tell us, it's not about iMovie, it's all about we all have to do by 'clouding' instead 'fooling around with idvds'. I can understand that's the policy against piratery but most people just want to make (family) discs for their own use!!
So fixing idvds is becoming a delicate matter today...
But Never give up, Brenda, finally you'll find the eureka! With or without help of these forums.