2.6.6 hangs indefinitely on "Encoding..."

[ProfessorProf]

Working with some .mp4 files that I had worked with without trouble on a Win7 laptop running avidemux 2.5.6. Now I'm on a Win8 laptop, running avidemux 2.6.6, trying to work with the same files for a bit of simple file trimming.

Video Output: Tried Mpeg4 (x264) and Mpeg4 (xvid4).
Audio Output: MP3 (lame)
Output Format: Tried MP4 Muxer and AVI Muxer.

Didn't touch any other settings, fresh install. When I try to save the file, a blank window titled "Encoding" pops up, and the program freezes until I force quit, even if the file is only a few seconds long.

[ProfessorProf]

Uninstalled 2.6.6 (32-bit) in favor of 2.6.1 (64-bit), same problem.