Follow below steps if you are hitting this kind of error while assigning roles to user.
Method 1
Execute transaction code PFCG and switch to User tab. Highlight the users listed and click on User comparison.
Click on Complete Comparison. Once done, you will see the User comparison tab become green.
Method 2
From the top menu of transaction code PFCG, go to Utilities > Settings. On the Settings: Role maintenance dialog box, select the option Automatic User Master Adjustment when Saving Role. Fyi, the saving might take a bit longer if you select this option.
Method 3
If you are having multiple roles, you may use the transaction code PFUD to do the mass user comparison.
Thanks. It was very useful