FATAL: erealloc(): Unable to allocate 83921 server Slow

[Savera]

Hi,

Suddenly my server started to get slow and  am receiving follow errors in my apache log :

Code: [Select]

FATAL:  erealloc():  Unable to allocate 81921 bytes
FATAL: emalloc(): Unable to allocate 5 bytes
FATAL: erealloc(): Unable to allocate 15360 bytes
FATAL: erealloc(): Unable to allocate 61440 bytes
FATAL: emalloc(): Unable to allocate 3840 bytes
FATAL: erealloc(): Unable to allocate 15360 bytes
FATAL: emalloc(): Unable to allocate 3840 bytes
FATAL: erealloc(): Unable to allocate 61440 bytes
FATAL: erealloc(): Unable to allocate 15360 bytes
My server specs are ,

Core2quad
4GB RAM
500GB SATA HDD
cPanel
Cent OS

What is the cause of error and how do I fix it ?