This issue typically occurs due to security restrictions related to the Odoo model 

res.users

.Even though you are a superuser or an administrator, access to certain records, like 

res.users

, may be implicitly restricted by record rules or group permissions. This often happens when specific access rules are altered or missing in the security settings.

For example, the "res_users all" access rights might have been changed from global to internal users only. As a result, portal users or other restricted users will face this issue when they attempt to access areas that implicitly depend on 

res.users 

records.

To resolve this, ensure that the necessary access rights are correctly assigned to the relevant user groups, especially for models like 

res.users

 that have strict security by default. This can be done through the Odoo interface in Settings → Technical → Security → Access Rights. Also, make sure that custom modules or rules aren’t overriding default access rights improperly.

In cases of multi-company setups, the issue can also arise if the user is not properly assigned to the right company during record creation​