Question, does the app crash without creating the epub (e.g. you get a 0-byte epub) or does it crash but you get a working epub? I just tried it on a Vista Home Premium laptop and the app crashed. When I checked the epub, though, it was working just fine (in Adobe Digital Editions, Calibre and Stanza).
I like using the PHP script better than converting within Calibre. If you look at the script (codec\epub.codec.php), you'll notice it embeds metadata into the epub and and prettifies chapter titles. Assuming I didn't break something in the code, that is.
By the way, you don't have to specify the output filename. I just do so since I like naming my files by story id (makes re-downloading easier in case of updates). If you leave out the output filename option from the command line, files will be named author_name_-_story_title by default.
I've got a bunch of concurrent versions of the PHP scripts (for testing and differing usage scenarios) and I'm going to need to consolidate them into as few versions as possible. Heck, I don't even know what version of epub.codec.php I uploaded. It might be one of the broken ones since my only concern when I uploaded the scripts is that it's usable with a Calibre recipe. epub generation wasn't exactly a requirement. After I do some code clean-up, I'll post a fixed/updated version of the script here.