Unable to use a trunk...? (Extremely odd)

[jmhadaller (Jessie M. Hadaller)]

I have a very strange situation.
Summary of configuration: 3 trunks. 1, inbound only, 2 in and out. You need to dial a 9 to dial out on trunk a, and no extra dial code is needed to dial out on trunk b.

Problem: In the morning, I am able to make calls through Trunk A&B perfectly fine. However, in the afternoon / evening is when I cannot make calls on trunk B.
When I look, I see errors of:
CHANUNAVAIL HANGUPCAUSE=21 (failing through other trunks)

The kicker: I have ZERO time conditions setup that would cause the issue.

This has been going on for WAY too long…

[dicko]

If your carrier returns a 21, only they can tell you why they rejected it. You can confirm that yourself with sngrep.