Make sure there is a mailbox for the A2E service account and it has been opened.

Make sure CDO has been installed on that replication server machine from the preinstaller directory

Make sure the server you are referencing is you exchange or cas or dag group name.

Make sure for the service account you are using just the name of the service account, or email address, not in the format domain\serviceaccountname

If none of these work, please submit a request and copy exact error. http://support.diditbetter.com/support-request.aspx

Hope this helps