NOTICE[510] pbx_spool.c: Call failed to go through, reason

Asterisk Asterisk Support
1

I place outgoing calls using call files. Once in a while calls fail with these messages:

NOTICE[510] pbx_spool.c: Call failed to go through, reason 3

sometimes

NOTICE[510] pbx_spool.c: Call failed to go through, reason 8

and

NOTICE[510] pbx_spool.c: Call failed to go through, reason 5

Can somebody explain and point me to an explanation of these reason codes?

Thanks