apache getting stuck after reaching max number of max clients

[val john <valjohn1647@xxxxxxxxx>]

Hi.. guys

My apache config as follows ,

#
Timeout 1000
KeepAlive Off
MaxKeepAliveRequests 500
KeepAliveTimeout 15

<IfModule mpm_prefork_module>
    StartServers          5
    MinSpareServers       5
    MaxSpareServers      10
    MaxClients           150
    MaxRequestsPerChild  500
</IfModule>

my apache getting stuck once hour due following error in the log [1], im using Debian 5  and have 4G   memory... , what can i  do for fix this issue..?   .

my memory is also  fully utilized ,

             total       used       free     shared    buffers     cached
Mem:          3962       3934         27          0        231       3167
-/+ buffers/cache:        534       3427
Swap:         8192          0       8192




[1]  Error
======
Thu Sep 27 18:25:42 2012] [error] server reached MaxClients setting, consider raising the MaxClients setting
[Thu Sep 27 18:29:08 2012] [error] [client 203.143.18.194] File does not exist: /htdocs
[Thu Sep 27 18:35:26 2012] [error] [client 203.143.18.194] File does not exist: /htdocs


Thank You
john