Failed to Distribute Activity - Email Already Exists

Good morning.  We are using Salesforce in conjunction with the CRM.  We have created Communication Plans, but the emails are failing in most cases, stating an error :12007EmailAlreadyExists.  And it says that the email is invalid.  The emails are valid and we can email the people individually without issue.  The error occurs when we are running the communication automation.  It's not on the Salesforce side either, the activities aren't making it past the CRM.  Does anyone have any ideas?  We are using Microsoft CRM with Ellucian Recruit.  I'm at a loss for getting this resolved, which is why I'm posting out here.  Any help would be greatly appreciated.

Thanks
Clare