[Evolution] Evolution error message

[Dabo <dboratav gmail com>]

Hello there :
I am on Evolution and Ubuntu 12.4
Evolution works fine, but each time I send an e-mail I get this message
which I need to dismiss :

The reported error was "Failed to append to
mbox:///home/david/.local/share/evolution/mail/local#Sent: Invalid
folder URI 'mbox:///home/david/.local/share/evolution/mail/local#Sent'
Appending to local 'Sent' folder instead.".

How can I fix it (and get rid of the message) ?

Many thanks,

Dabo