Network Connectivity - Inbound calls failing on PRI Gateways

When inbound calls are failing on G100, G200, and G400 PRI Gateways, but outbound calls work:
Run a PRI debug on the Gateway.
Check for responses from the Gateway like this:

chan_gtw/sig_pri_new.c:1106 in sig_pri_is_chan_available:     -- prioffset 1, logicalspan 0, trunkgroup 1 is in use, NOT out of service, 
chan_gtw/sig_pri_new.c:5032 in pri_dchannel: Group 1: SETUP requested unavailable channel 0/1.  Attempting to renegotiate. 
chan_gtw/chan.c:4803 in dgm_pri_message: port1 >                  Ext: 1  Cause: Requested channel not available (44), class = Network Congestion (resource unavailable) (2) ] 

If the Gateway immediately hangs up on inbound call and it shows channel is unavailable, in the PRI debug, check the following settings in the Gateway:
Go to Configuration > T1/E1 > Port1 > Advanced Signaling > Idle Bearer Reset set to NO (this should be the default setting). Save T1/E1 Settings. Do this for each port, if there is more than one port on the gateway.  

If there is still an issue, try to disable FORCERESTART_UNAVAIL_CHANS on same page (Configuration > T1/E1 > Port1 > Advanced Signaling ), although it is unlikely this is causing the issue.