Reddit conversation: https://www.reddit.com/r/Fez/comments/4i9mjn/i_need_some_help_in_using_fezviewer/d3176br

There seems to be an issue with using xnb_parse on non-western Windows systems. As seen in Pimez's screenshot, the "pause" text (after I told him to add two pause statements to catch a screenshot) indicates an eastern Windows locale.

After moving the xnb_parse folder to C:\ as workaround and running it there, it worked for Pimez, further confirming that it's a file path issue.