Thanks for you replay.
I check the permissions of the data folder, they are set on 755. i tried with 777 but works not.
the settings are correct.
in the log file, i found this:
[22-Jun-2010 11:02:36 +0200]: IMAP Error: Could not save message in Sent in /home/princeprojects.com/public_html/crm/modules/CRM/Roundcube/src/program/steps/mail/sendmail.inc on line 620 (POST /crm/modules/CRM/Roundcube/src/?_task=mail&_action=send)
it's only happens when i send a email with a attachment. without a attachment it works correct.