I just posted a bug-fix release (v1.32). There seems to be an issue with people who run k2pdfopt in locales where the decimal marker is a comma rather than a period (e.g. most European and Latin-American countries). It results in output PDF files that are often unreadable. I think this was introduced in v1.31 with the DJVU library, but I'm not sure. Hopefully it is fixed now.
http://willus.com/k2pdfopt/
Sorry for the inconvenience this has caused. Thanks to SkyDream for helping me figure this one out.