I am using a 12.6 SP1 Policy Server and Web Agent 12.52 SP1 CR00 (GA).
I am receiving the below error while registering the Web Agent with the Policy Server:
" Registration failed: Unable to connect to policy server"
There are not network issues between the Policy Server and the Web Agent.
IIS 8.5 is only supported with Web Agent 12.52 SP1 CR2 and above:
https://support.ca.com/phpdocs/7/5262/5262_SiteMinder_12_52_SP1_Platform_Support.pdf (page 21)
Download and install Web Agent 12.52 SP1 CR2 and above to solve this issue.