If you are getting horde session handler error, then please check if horde db is present on server or not. You can check it with

#mysqlshow |grep horde
It should give you output like,

[~]#mysqlshow |grep horde
| horde |

If the output is blank, then you need to create a db called horde.
You can do it with commnd.
#mysqladmin create horde

Then run a script :
#/scripts/fullhordereset

If horde db is already exist on server then go to mysql and on mysql prompt run commands.

mysql>use horde;
mysql>repair table horde_sessionhandler;
mysql>\q

Then on shell prompt run commands
#touch /var/cpanel/usecpphp
#/scripts/fullhordereset

It will fix the most of issue with horde.