Outlook Converting font to OPEN SANS in Reading Panel

[jlh]

I'm using Outlook 10. Some time back, months ago, Outlook started converting random messages from my default font to OPEN SANS font, which is a tiny script that is impossible to read. I can't find Open Sans anywhere on my computer so I don't know where Outlook is getting it. I've searched everywhere for an answer but can't solve the mystery. I've reset my default prompt many times but that doesn't help. I can open the message, edit it, and change the font and save it and it's fine. I just can't figure out why Outlook started using Open Sans and how to make it stop. Thanks for any help.