The Server encountered an error while trying to retrieve the Certificate Trust List
To resolve this issue execute the following steps:
Either the root CA has been taken offline for security reasons or the client's certsrv can't locate the CRL's. By default the Cert srv publishes a new revokation list every 7 days. If your root CA were taken offline and the new CRL wasn't published online to AD, your cert chain will be broken.
Check the respective Items.