Thanks for the OS X version (finally! I've been waiting a year for it). When I tried to download it using the Safari browser (THE default browser for Mac users, since Microshaft has decided it will no longer support IE for the Mac), the pop-up window asking for the user ID and password did not function, and the Safari program locked up. I was able to download it successfully with my old version of IE.
You should either (a) make your website compliant with the Safari browser that Mac users use, since you are selling Mac software; or (b) inform users in your email instructions that the download won't work with Safari, and list browsers that do work (I didn't try any others besides IE, but I'm sure you can test other options, like Netscape or Mozilla).
Mac OSX version download issues
Re: Mac OSX version download issues
It looks like a plain vanilla HTTP Basic Authentication scheme, which should work in any browser. It works fine in Firefox under Windows XP as well as Galeon under FreeBSD. Perhaps try Firefox under OS X and see what happens there.
NeatImage Pro Plus 5.0 + dual Opteron 244 + Windows XP SP2 + FreeBSD 5.2