Hello guys! I think I have reached a breakthrough here!
I also got "unspecified error", luckily already at 0.2 % encoding. Having that error at 99 % would be terrible annoying! To find the reason for this error, I had to move back to Windows Movie Maker and choose “Publish to my computer” instead of “Publish to DVD” to track the cause of this error. The “unspecified error” in DVD Maker seems to be closely related to the "Cannot complete publish movie" (in spite of the fact that I had plenty of space on my hard drive etc.) in Movie Maker. As long as I had the latter error in Movie Maker, the former error was shown in DVD maker.
I discovered that Movie Maker was able to publish my movie to the computer after I removed all the pictures I had placed between the movie clips. I also discovered that pictures that had the resolution 2560x1920 (width x height) pixels could be included in the video without causing error! That is, after removing all pictures that did not have the resolution 2560x1920, the movie could be published without error!
Still, I wanted to use all my pictures and therefore scaled all pictures to 2560x1920 (all of them had lower resolution in advance) in Microsoft Office Picture Manager. And “voila”! Now Movie Maker was able to publish to my computer, and DVD maker was also able to publish to DVD!
Why Movie Maker can’t handle pictures with resolution below 2560x1920 is to me a mystery. But I don’t care anymore. The only thing that matters is that Movie Maker and DVD Maker is back on track! (at least for me…)
Hope this works for you too!