I replied in haste... This error indicates you might need to run keychain
first aid. This is a pretty typical error.
Send & Receive Basics:
1. If you can receive but not send then you have a bad SMTP configuration
2. If you can send but not receive you have a bad POP or IMAP configuration
You can try re-entering info.
You can delete account and create a new one.
Using copy/paste can result in an extra space being added. Type carefully.
Check your Keychain for corruption.
Keychain First Aid:
Run Keychain Access found in /Applications/Utilities/Keychain Access.
Go to the Keychain Access Menu and drag down to Keychain First Aid.
Enter your login password, click 'Verify' and 'Start'.
You will probably get some items colored red. Click 'Repair' and 'Start'. If
some items are still red, 'Repair' again.
Test to see if the problem is fixed. If not...
1. Go to the system keychain and delete the entry for that account.
2. Go to Entourage, select 'accounts' from the Tools menu, choose the
account that was giving you trouble and click on Edit. Select the 'account
settings' tab.
3. Delete the password from the password box in the POP settings (leaving
the box empty).
4. Close the account window.
5. Re-open the account window and enter your proper password, check the
'save in keychain' check box and close the window again.