1. Disable INET_Dns_Domain.km
The reason for this failure can sometimes be the INET_Dns_Domain.km which is an old part of the ISM KM and can be disabled without loss of function.
2. Another possibility is that user have configured the ISM KM incorrectly. Perhaps specified HTTP instead of HTTPS for an SSL/TLS site.
For other possibilities check these articles:
https://selfservice.bmc.com/casemgmt/sc_KnowledgeArticle?sfdcid=000118622
https://selfservice.bmc.com/casemgmt/sc_KnowledgeArticle?sfdcid=000015716