I am getting this error when I am trying to make foreign key relationship?

Question

I am getting this error when I am trying to make foreign key relationship :

As soon as I click on save, this error occurs :-

The ALTER TABLE statement conflicted with the FOREIGN KEY constraint "FK_tb_stadmdet_tb_prgdet". The conflict occurred in database "admission", table "dbo.tb_prgdet", column 'prgcod'.

Can anybody help me out with this problem, THANKS