Are you accessing it through Outlook or the browser on your pc because CompuServe is a pop server based account it should be able to use the same settings you use in Outlook, if you use the HTTP (Web Browser) version you may have to contact CompuServe for the correct settings.
Here is setting for... Try using the incoming and outgoing settings..
Microsoft Office Outlook 2007
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I have my account set up without Outlook using an IMAP server setting. You can find instructions at the following site: https://motorola-global-portal.custhelp.com/app/answers/detail/a_id/48924/~/droid---aol-email-set-up
The interesting thing is that the server setting used to be imap.cs.com but without any announcement, it has changed to imap.aol.com. If you use this server address for both outgoing and incoming settings, it will work.