No D-channels available!

Hello, everyone.
This is an incident that have occured today in my installation. I’ve got a ’ No D-channels available!’ message in a log. Since then nobody could make or receive calls. For every Dial asterisk was making, I was getting “Unable to create channel of type ‘Zap’ (cause 34 - Circuit/channel congestion)”. After restarting asterisk and zaptel everything went back to normal. It is not the first time this is happening (approximately every 2 weeks). Please, help me resolve this.
Thanks in advance.

PS. Lately I’m also getting ‘HDLC Bad FCS’ messages about every 2 seconds. I don’t know if this is related.

Nov 16 06:58:32 NOTICE[5832] chan_zap.c: PRI got event: HDLC Abort (6) on Primary D-channel of span 2
Nov 16 06:58:35 NOTICE[5832] chan_zap.c: PRI got event: HDLC Abort (6) on Primary D-channel of span 2
Nov 16 06:58:39 NOTICE[5832] chan_zap.c: PRI got event: HDLC Abort (6) on Primary D-channel of span 2
Nov 16 06:58:39 NOTICE[5832] chan_zap.c: PRI got event: HDLC Bad FCS (8) on Primary D-channel of span 2
Nov 16 06:58:39 NOTICE[5832] chan_zap.c: PRI got event: HDLC Bad FCS (8) on Primary D-channel of span 2
Nov 16 06:58:39 NOTICE[5832] chan_zap.c: PRI got event: HDLC Bad FCS (8) on Primary D-channel of span 2
Nov 16 06:58:46 WARNING[5831] chan_zap.c: No D-channels available! Using Primary channel 16 as D-channel anyway!
Nov 16 06:58:48 WARNING[5832] chan_zap.c: No D-channels available! Using Primary channel 47 as D-channel anyway!
Nov 16 08:11:13 NOTICE[29507] app_dial.c: Unable to create channel of type ‘Zap’ (cause 34 - Circuit/channel congestion)
Nov 16 08:11:38 NOTICE[29616] app_dial.c: Unable to create channel of type ‘Zap’ (cause 34 - Circuit/channel congestion)

Forgot to add:
zaptel.conf
span=1,1,0,ccs,hdb3,crc4
span=2,0,0,ccs,hdb3,crc4
span=3,0,0,ccs,hdb3,crc4 <- not used
span=4,0,0,ccs,hdb3,crc4 <- not used

As one of the advices to solve this I’ve seen: resetinterval=never. I do have it in zapata.conf.