CRUD Operation DELETE not work

I had add one table and mapped with database.

When i delete one record with that table i got one error "The object cannot be deleted because it was not found in the ObjectStateManager.".

I had pass data like below and delete function click.

userMaster.Id = 3;
_userMasterService.DeleteUser(userMaster);

Please help if anyone know.

I think there are some error in mapping with database.
Give me more information (class Entity and Class Map).