This would appear to be another example of a known issue. For More Information see: Send Mail using Outlook 2010 Error
This is one of many acknowledged bugs that can be found in the Known Bug List thread here in the Report an Issue section of the forum.
It can also be downloaded as a database file from: https://www.dropbox.com/s/jt09b82i0xijbu3/FMP%20Bugs.zip
Thank you for your post.
The information provided by PhilModJunk is correct (Thank you).
I have attached your post to the original report, and when any additional information becomes available, I will let you know.