Getting bizarre error message from Mail I have Mail set up to handle two different accounts: [my name]_iCloud, and [my name]_Gmail. 

Today, when I try to send a message from the iCloud account, I get this message:

Can't Connect to the account "[my name]_iCloud".
Enter the password for user "".

The message is exactly as I typed -- it does not provide the user name (which would've been [my name]@icloud.com). Just two quotation marks next to each other. Entering the iCloud password does nothing. It refuses to send any mail.

The iCloud account will RECEIVE messages. 
The Gmail account will both send and receive messages as usual. 

Tried deleting the iCloud entries in keychain. Did not work.

Any suggestions on how to fix this?
For the record, the problem appears to have been resolved. Steps I took to fix:

(1) Delete everything from key chain
(2) Remove gmail account from Mail.
(3) Restore gmail to Mail.

Everything works again. For now.