QuEnc is launched, before DVD authoring step, to create the motion DVD menu, if that option is selected. Otherwise QuEnc is not called. No differences between 2.3.4 and 2.4.x releases about that.
Probably with the newer releases (I don't know why, the log could help more), there are some issues when creating DVD menu thumbnails or background images (bmp), just before starting to create the motion DVD meu (m2v) with QuEnc.
Do you get same error using static DVD menu?
Bye