(11)Resource temporarily unavailable: couldn't spawn child process:

[KatieBuller]

Why am I getting this error?
(11)Resource temporarily unavailable: couldn't spawn child process:

php scripts are giving 500 errors and the error log shows:
(11)Resource temporarily unavailable: couldn't spawn child process:

Nothing appears to be written to swap:
# free -m
total used free shared buffers cached
Mem: 1991 1958 32 0 112 1526
-/+ buffers/cache: 320 1671
Swap: 4094 0 4093

Is this bad?

[kris1351]

Your server load is so high it cant spawn a process for the command you are running.

[webignition]

Searching Google for:

"Resource temporarily unavailable: couldn't spawn child process:"

either with or without the quotes will return many pages of useful information.