https://github.com/openhab/openhab/issues/992

Acording to http://msdn.microsoft.com/en-us/library/windows/desktop/aa365247(v=vs.85).aspx the following are reserved names and cannot be used as a filename (even with a extension)
CON, PRN, AUX, NUL, COM1, COM2, COM3, COM4, COM5, COM6, COM7, COM8, COM9, LPT1, LPT2, LPT3, LPT4, LPT5, LPT6, LPT7, LPT8, and LPT9.