Ok, I threw caution to the wind, activated Windows Live on my Windows 7 (x64) machine, made it the default email client, and took a screen picture. After clicking the email button, it launched Windows Live with the message, including the png image as an attachment (shown in the header below the Subject like, not embedded in the body). And when I sent it, it all went just as it should (arriving in Thunderbird as a normal message with an image attachment.)
So it sounds to me like a Windows Live configuration problem relating to the format of the messages or how images are attached. I looked through the Options and Properties dialogs, but couldn't find any such option.
However, an Internet search revealed this About.com link:
How to disable inline display of image attachments in Windows Mail, Live Mail I do not have the item they suggest adding (HKCU\Software\Microsoft\Windows Live Mail\Automatically Inline Images), and in any case the article seems to be concerned more with receiving messages than sending them, so I'm not sure this is quite the solution. But I did note that I had the following two attachment-related registry items, both set to 0x00000001:
Safe Attachments
Secure Safe Attachments
Maybe those are significant, maybe not.
I also searched for "Windows Live Mail delete the photo email" and got several forum hits referring to the exact message you got, most of which seem to suggest that the problem was due to the skydrive being disconnected, or a problem with the outgoing server, etc.
I would suggest some poking through those forums to see if any of the tips help you resolve the issue. At this point, it does not appear to be an issue with A-Shell itself.