Help solving warnings!.

[nsolano@cima.tij.uabc.mx]

Hi, we have a linux mandrake 8 mail server postfix with IMP 2.2.4 and horde 
1.2.4,  we also have installed amavis with nai antivirus. 

Lately, when we access the IMP web page, what we see are next warnings:

Warning: not enough shared memory left in /var/www/horde-phplib/ct_shm.inc on 
line 54

Warning: Cannot add header information - headers already sent by (output 
started at /var/www/horde-phplib/ct_shm.inc:54) in /var/www/horde-
phplib/session.inc on line 120

Warning: variable key 99 doesn't exist in /var/www/horde-phplib/ct_shm.inc on 
line 79

We'll appreciate any help. Thanks.