Understanding why you are unable to change the security settings on an Active Directory organizational unit is an important first step to resolving the issue. Follow the steps below to determine the cause and appropriate solution:

1. Verify you have the appropriate permissions to make the desired changes
2. Ensure the settings are accurate and compatible with the underlying server OS
3. Check for any underlying issues, such as network or configuration issues, that may be preventing you from mkaing the necessary changes
4. Contact technical support, if needed, to discuss the issue and resolve it