Because they use dumb anti-virus tools and block file types, like .com, .exe, .vbs, .pif, etc. regardless of the fact that the file is legit or not infected.

I had a similar problem with my smtp mail provider, they refused to send an email with an attachment with an .exe file type. I sent a windows update patch (which is a self-extracting [.exe] file) to a friend with a problem. XP Pro wouldn’t let me zip the .exe file.

At lease they had the common sence to at least tell me they had blocked it.

I got around the problem by moving the .exe file to a temp folder and zipping that and low and behold no problem with the zip attachment, so dumb antivirus policy.

David