"Invalid Action" Error When Accessing CSP

I’m facing an issue with a CSP-based web application.
The default.csp page loads correctly on both servers. However, when I try to open or submit the login.csp page on one server, it shows the error:

"INVALID ACTION"

The exact same codebase is deployed on another IRIS server, and it works there without any issues.

Summary of the issue:

• default.csp → Loads successfully
• login.csp → Fails with “INVALID ACTION” only on one server
• No code changes between the two servers

Has anyone encountered this kind of scenario?
What configuration differences should I check between the two servers that might cause this behavior?