The most recent version (4.5.1.166) fixes the "Zero byte file crash", please go to <http:> for downloading (sorry, no hyperlinking possible in comments).</http:>

    Extension Development Kit for WinPMail v2.0 and later.
                     Pegasus Mail System,
    Copyright (c) 1990-96, David Harris, All Rights Reserved.

This ZIP file contains two files - this Readme file, and a file called
FORMS240.ZIP, which contains the current version of the Extension
Development Kit.

(Not usually required unless you are using Pegasus Mail v3.x or

earlier)