I am having the same problem and cannot add an image to an email overall - signature line or body of email. I am using Outlook 2010, not OWA. The error that I get is:
[cid:image001.jpg@01CDB8F0.709F6AD0]<issuu.com/.../120828162445-d1b8b896a41e4945a5b069e01f3741f7