How is the user trying to access Rewards? Is it by going directly to the URL or does the non-admin user see the rewards option from the dropdown menu?
Admins with Manage System permissions and higher, should have the option to view rewards. The other, non-admin users should not see the option, similar to mine below:
However if non-admins are seeing the option for rewards and receiving the error, we will likely need a support case in your Private support group so that Support perform a deeper investigation and can review the specific errors for your instance.
Hope this helps.
I don't know why but it's working today.
Thank you for your help,