Try following command to fix the issue
root@server[~]#/usr/local/cPanel/bin/checkperlmodulesroot@server[~]#/scripts/fullhorderesetroot@server[~]#myisamchk -r /var/lib/mysql/horde/horde_sessionhandler.MYI
If still you have problem then check the ownership for session directory present in /var/cpanel/userhomes/cpanelhorde directory.
root@server[~]#ll /var/cpanel/userhomes/cpanelhorde
drwx–x–x 4 cpanelhorde cpanelhorde 4096 June 5 2012 ./drwx–x–x 7 root root 4096 Dec 17 01:48 ../drwxr-x— 2 cpanelhorde cpanelhorde 4096 June 5 2012 mail/drwx—— 2 cpanelhorde cpanelhorde 4096 Jan 27 14:01 sessions/
Session directory should be cpanelhorde.cpanelhorde ownership recursively