When a User attempts to go to Setup, My Profile, or My Settings they receive an 'Insufficient Privileges' message.
This may occur if the Api Only User is enabled by checking the box for Api Only User in either the User's profile permissions or in a permission set that is connected to the User.
You can resolve this issue by disabling the Api Only User option. To do this, check the User's profile to see if this feature is enabled (see steps below.) If the 'Api Only User' option is not enabled at the profile level, then look at the 'Permission Set Assignments' related list to find the permission set that has been configured with this option. Then disable it there (see steps below.)
Note: When troubleshooting this problem, doing a log in as for the User will not cause the 'Insufficient Privileges' message. It may seem like everything is okay from the administrator's perspective when using the log in as feature, however when the User goes to log in they will still experience this error.
If you still experience the issue after reviewing both options presented above please contact Salesforce Support.
See also
Create a secure Salesforce API user
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