Hi Randy. Go to Settings >> Log Settings, and make sure ActiveSync logging is set to detailed. Then once this error occurs, look in the ActiveSync logs for any Exceptions or SYNC KEY MISMATCH errors.
If those are found, then impersonate the end-user and go to Settings >> My Settings >> Synchronized Devices. Delete the devices. Afterwards, remove and re-add the EAS profile within the email client. I think that should take care of this.
Technical Support Specialist