Hello everyone,
I'm trying to convert HDR to RAT format but I get this error in command line “Can't create output file fileName.rat”. I run Command Line Tools as administrator.
Also I've done this in mPlay and it works perfectly(with limitations)

Windows 8.1
Houdini Apprentice v13.0.570

With apprentice version, your images should be not larger than 960x720 in resolution.