Competency validation on update appraisal user hook not working as expected

We have a requirement in oracle performance management EBS for competency validation. The number of competencies to be chosen should be minimum of  4 competencies.

if the employees choose less than 4 competencies, system should throw an error. We tried using appraisal user hook to do the validation but it is not working as expected.

if competencies chosen are less than 4 and we try to add the competencies using "Add Competencies" button. system will not allow to add.

Any ideas on this would be appreciated.

Thanks for help in Advance!

Regards,

Seetha