LinuxQuestions.org - Cannot allocate memory: couldn't spawn child

I get this error a lot in apache1 error_log. Refreshing the website usually makes it work though. I think it has something to do with PHP, because it happens on several php programs

"Cannot allocate memory: couldn't spawn child"

Here is a part of the log:

/buymoco/public_html/web/imgsrv.php
[Mon Jan 9 10:35:55 2006] [error] [client 216.183.106.196] (12)Cannot allocate memory: couldn't spawn child process: /home/buymoco/public_html/web/imgsrv.php
[Mon Jan 9 10:35:55 2006] [error] [client 216.183.106.196] (12)Cannot allocate memory: couldn't spawn child process: /home/buymoco/public_html/web/imgsrv.php
[Mon Jan 9 10:35:56 2006] [error] [client 216.183.106.196] (12)Cannot allocate memory: couldn't spawn child process: /home/buymoco/public_html/web/imgsrv.php
[Mon Jan 9 10:35:57 2006] [error] [client 216.183.106.196] (12)Cannot allocate memory: couldn't spawn child process: /home/buymoco/public_html/web/imgsrv.php
[Mon Jan 9 10:36:23 2006] [error] [client 216.183.106.196] (12)Cannot allocate memory: couldn't spawn child process: /home/buymoco/public_html/web/staff.php
[Mon Jan 9 10:43:21 2006] [error] [client 206.72.71.164] (12)Cannot allocate memory: couldn't spawn child process: /home/powerhou/public_html/index.php
[Mon Jan 9 10:44:57 2006] [error] [client 216.89.132.163] (12)Cannot allocate memory: couldn't spawn child process: /usr/local/frontpage/version5.0/apache-fp/_vti_bin/fpexe
[Mon Jan 9 10:46:11 2006] [error] [client 69.152.92.230] (12)Cannot allocate memory: couldn't spawn child process: /home/buymoco/public_html/web/imgsrv.php
[Mon Jan 9 10:46:12 2006] [error] [client 69.152.92.230] (12)Cannot allocate memory: couldn't spawn child process: /home/buymoco/public_html/web/imgsrv.php
[Mon Jan 9 10:46:15 2006] [error] [client 69.152.92.230] (12)Cannot allocate memory: couldn't spawn child process: /home/buymoco/public_html/web/imgsrv.php
[Mon Jan 9 10:46:38 2006] [error] [client 69.152.92.230] (12)Cannot allocate memory: couldn't spawn child process: /home/buymoco/public_html/web/index.php
[Mon Jan 9 10:54:16 2006] [error] [client 66.249.65.34] (12)Cannot allocate memory: couldn't spawn child process: /home/powerhou/public_html/index.php
[Mon Jan 9 10:55:52 2006] [error] [client 70.27.89.110] (12)Cannot allocate memory: couldn't spawn child process: /usr/local/frontpage/version5.0/apache-fp/_vti_bin/fpexe
[Mon Jan 9 10:59:54 2006] [error] [client 216.124.245.107] (12)Cannot allocate memory: couldn't spawn child process: /usr/local/frontpage/version5.0/apache-fp/_vti_bin/fpexe
[Mon Jan 9 11:02:21 2006] [error] [client 65.68.150.12] (12)Cannot allocate memory: couldn't spawn child process: /home/squirrelmail-1.4.4//index.php
[Mon Jan 9 11:02:37 2006] [error] [client 65.68.150.12] (12)Cannot allocate memory: couldn't spawn child process: /home/squirrelmail-1.4.4//src/webmail.php
[Mon Jan 9 11:17:32 2006] [error] [client 71.14.68.232] (12)Cannot allocate memory: couldn't spawn child process: /usr/local/frontpage/version5.0/apache-fp/_vti_bin/fpexe
[Mon Jan 9 11:27:38 2006] [error] [client 4.244.147.14] (12)Cannot allocate memory: couldn't spawn child process: /usr/local/frontpage/version5.0/apache-fp/_vti_bin/fpexe
[Mon Jan 9 11:29:06 2006] [error] [client 65.68.150.12] (12)Cannot allocate memory: couldn't spawn child process: /home/squirrelmail-1.4.4//index.php
[Mon Jan 9 11:29:21 2006] [error] [client 65.68.150.12] (12)Cannot allocate memory: couldn't spawn child process: /home/squirrelmail-1.4.4//src/right_main.php
[Thu Jan 12 08:09:21 2006] [error] [client 69.150.82.28] (12)Cannot allocate memory: couldn't spawn child process: /home/squirrelmail-1.4.4//src/compose.php
[Thu Jan 12 08:23:44 2006] [error] [client 69.150.82.28] (12)Cannot allocate memory: couldn't spawn child process: /home/squirrelmail-1.4.4//src/printer_friendly_bottom.php
[Thu Jan 12 08:27:46 2006] [error] [client 66.249.65.34] (12)Cannot allocate memory: couldn't spawn child process: /home/shanewf/public_html/photos/displayimage.php
[Thu Jan 12 08:50:17 2006] [error] [client 65.68.150.12] (12)Cannot allocate memory: couldn't spawn child process: /home/unity/public_html/cgi-bin/sawmill/sawmill.cgi
[Thu Jan 12 08:50:18 2006] [error] [client 65.68.150.12] (12)Cannot allocate memory: couldn't spawn child process: /home/unity/public_html/cgi-bin/sawmill/sawmill.cgi
[Thu Jan 12 08:52:00 2006] [error] [client 65.68.150.12] (12)Cannot allocate memory: couldn't spawn child process: /home/unity/public_html/cgi-bin/sawmill/sawmill.cgi