Network traffic is blocked even though a custom firewall rule has been created that should allow it, and the firewall rule is set to secure to allow custom rules to overrule default rules.
Make a copy of the default block rule and switch it to allow.
login to SEPC.
Go to Policies>Security Policy
Select the desired policy to edit, or create a new security policy (NOTE: the Symantec Recommended Policy cannot be modified.)
Go to the Network Protection section of the policy.
Check the box for "Show Default Rules"
Scroll until you find the role you've determined to be blocking the desired traffic.
Select the Rule. Switch the connection from "Block" to Allow".
Save the Rule.
Save the Policy.
Test to ensure the desired traffic is now being allowed.