"Could Not Open Attachment"
What is that all about? I am not attaching anything! Seems odd doesn't it? It all boils down to how Eudora operates. At times messages are not sent, but queued to be sent. This is where the problem lies. Never fear though, easily enough fixed
Get rid of offending item(s)
You have a message in your Out mailbox that has been queued to be sent, but is linked to an attachment which no longer exists.
1.Open up your Out mailbox and search for any messages that have a "Q" in the status column.
2. Delete any of these.