This error is valid for version R75.20, R75.30, R75.40
Installation failed; reason - load on module failed, failed to load security policy
You are getting this error , because of defining new URL site.
To solve this issue;
Open smartdashboard ;
Application & URL Filtering --> Application / Sites --> Edit the custom application/site that you have created and Uncheck the URLs are defined as Regular expression.
Try to install policy again.