This problem occured in the web browser when i was trying to access our open web mail. One thing is that openwebmail puts users uploaded attachments in cgi-bin/openwebmail/etc/sessions. Users will normally get this error if there is no space left on the partition where cgi-bin/openwebmail/etc/sessions lives or user has exceeded his disk quota.
To solve this, please move cgi-bin/openwebmail/etc/sessions to a larger partition. Then create a symbolic link to that new directly.
Steps as above
That is change directory to the new big disk space.
Create a directory called “sessions” in this new big disk space
Create a directory directory called “sessions” this new big disk space.
chmod 770 sessions
Change the mode of the directory “sessions” which was just created.
chown 0 sessions
Change ownership of the “sessions” directory created.
chgrp mail sessions
Add sessions directory created to the mail group.
Change directory or move into were your openwebmail/etc is.
cp -rf sessions
Make backup of sessions directory in the “etc” to somewhere safe.
rm -rf sessions
Delete the sessions in the yourweb_cgi-bin/openwebmail/etc
ln -s /new_place/sessions .
Still in the “yourweb_cgi-bin/openwebmail/etc” directory, create a symbolic link.