I noticed the other day that when I tried attaching a pic with the "Attachments" button, I got some error, something about it not meeting security requirements or something.
If you upload your pictures to a photo-hosting website like photobucket, and then use the html code to attach it, you shouldn't have any problems. After you upload the picture, hover your cursor over it, and a box will pop up showing the "IMG Code". If you click on the text in the white box beside that, it will copy it. Then just paste that into your message.