This is not an error. This is a function of Performance of Review. If you receive this message in Performance Review, you have incorrectly set admin rights for your employees.
You will need to log in as a user that is NOT administrator to perform the review.
To correct your settings and resolve this error message, create or edit an employee so that they do not have admin rights. The Admin box in Employee Info should be un-ticked. Note the log in information for the user. Exit the program and re-launch it, this time using the non-admin user log in. This user will be able to perform appraisals.