http://bugs.winehq.org/show_bug.cgi?id=30819
--- Comment #5 from Alejandro Nova alejandronova@gmail.com 2012-06-01 17:22:49 CDT --- It seems a 0 byte file with the extension .M50all would be enough to trigger this.
You can download some valid files for the M50 here: http://www.korgcanada.com/eng/support/downloads/zips/M50ProVintageKeys.zip