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.
Sorry for the inconvenience this has caused. Thanks to SkyDream for helping me figure this one out.