When you are a member of the built in Security Administrators role, you are unable to add another user to the same role in K2 Management > Users > Roles.
- Ensure you have K2 Five (5.1) installed.
- Get the K2 Five (5.1) FP11 from Regional Support.
- Install the K2 Five (5.1) FP11 to apply the fix.
- It is recommended to refresh the browser cache.