Hi Jeff,
Were you able to get a resolution to this issue? We are also getting the same error on some emails.
I did check Note # 185098 http://service.sap.com/sap/support/notes/1858098 but we already have it as part of the CRM 7.0 SP07.
Check it out, if that helps in your case. Also, if you already had a solution on this, please share.
Thanks,
Lankesh