Unable to reissuing certificate. How can we solve this?

2017/04/19 15:26:40 [error] 5547#0: *1155021 [lua] lets_encrypt.lua:32: issue_cert(): auto-ssl: dehydrated failed: env HOOK_SECRET=c2d5f64508a4c2edee0c4faf1c19f3f81908264232eb56b23d9602cd4bfaef36 HOOK_SERVER_PORT=8999 /usr/local/share/lua/5.1/resty/auto-ssl/vendor/dehydrated --cron --no-lock --domain www.imagecon.com --challenge http-01 --config /etc/resty-auto-ssl/letsencrypt/config --hook /usr/local/share/lua/5.1/resty/auto-ssl/shell/letsencrypt_hooks status: 256 out: # INFO: Using main config file /etc/resty-auto-ssl/letsencrypt/config
Processing www.imagecon.com
+ Checking domain name(s) of existing cert... err: # !! WARNING !! Extra configuration directory /etc/resty-auto-ssl/letsencrypt/conf.d exists, but no configuration found in it.
unable to load certificate
140039407040152:error:0906D06C:PEM routines:PEM_read_bio:no start line:pem_lib.c:701:Expecting: TRUSTED CERTIFICATE
, context: ssl_certificate_by_lua*, client: 10.169.165.199, server: 0.0.0.0:443
2017/04/19 15:26:40 [error] 5547#0: *1155021 [lua] ssl_certificate.lua:88: issue_cert(): auto-ssl: issuing new certificate failed: dehydrated failure, context: ssl_certificate_by_lua*, client: 10.169.165.199, server: 0.0.0.0:443
2017/04/19 15:26:40 [error] 5547#0: *1155021 [lua] ssl_certificate.lua:247: auto-ssl: could not get certificate for www.imagecon.com - using fallback - failed to get or issue certificate, context: ssl_certificate_by_lua*, client: 10.169.165.199, server: 0.0.0.0:443

Start with the dehydrated output and the referenced locations lets_encrypt.lua:32 and ssl_certificate.lua:88/247, then trace the certificate-loading and reissuing path for www.imagecon.com. Reproduce the failure and identify why the existing certificate cannot be loaded; done means certificate issuance succeeds without falling back to the fallback certificate.

Written by the indexing model from the issue text.