Relationship Problem in SQL (Column can't be cascaded)

Question

I have 3 tables (Patient,Doctor,Appointments) patient has a primary key(Patient_ID)and a foreign key (Doctor_ID) Doctor has a primary key(Doctor_ID) Appointments has a primary key(Appo_ID)and two foreign keys(Patient_ID,Doctor_ID) here is the problem,In the relationship diagram the two relations(Patient.Patient_ID,App.Patient_ID & Doctor.Doctor_ID,Appo.Doctor_ID) can't be cascade at once, if one is cascade, the other show this error message

- Unable to create relationship 'FK_Appointments_Doctor'.  
Introducing FOREIGN KEY constraint 'FK_Appointments_Doctor' on table 'Appointments' may cause cycles or multiple cascade paths. Specify ON DELETE NO ACTION or ON UPDATE NO ACTION, or modify other FOREIGN KEY constraints.
Could not create constraint. See previous errors.

and this is my procedure for updating

ALTER PROCEDURE UpdateDoc
    @Doctor_ID INT,@Name NVARCHAR(50),@Salary MONEY,@Hire_Date DATETIME,@Dept_ID INT,@Old_ID int
AS

    Update Doctor
    Set 
        @Old_ID=Doctor_ID,
    Doctor_ID=@Doctor_ID,
    [Name] =@Name,
    Salary=@Salary,
    Hire_Date=@Hire_Date,
    Dept_ID=@Dept_ID
    Where Doctor_ID=@Old_ID
Return

If there any question for more specific, ask me

Answer 1

It's a cyclic dependency, why would you want it to cascade? And why are you updating the Doctor_ID strictly speaking you shouldn't ever be updating (setting) the primary key.

That you are filtering Where Doctor_ID=@Doctor_ID on the same value you are updating Set Doctor_ID=@Doctor_ID tells me you haven't tought this through.