Not sure if this is the right forum?

I have two tables as below. I want to update a quote and change the item for which it is for. So I want to do an update statement to change the cat_ref that the quote is for. However, when I do this I get a foreign key conflict with cat_ref in the item table. How do I get around this? Thanks

Code:
CREATE TABLE Item (	
	cat_ref VARCHAR(5)PRIMARY KEY,
	descrip VARCHAR(50), 
	date_added SMALLDATETIME,
	cat_type VARCHAR(20),


CREATE TABLE has_quote (	
	quote_id INT IDENTITY (1,1) PRIMARY KEY,
	date_of_quote SMALLDATETIME,
	cat_ref VARCHAR(5)FOREIGN KEY 
		REFERENCES Item(cat_ref),
	first_name VARCHAR(10),
	surname VARCHAR(10),
	customer_phone VARCHAR(20),
	FOREIGN KEY (first_name, surname, customer_phone) 
		REFERENCES Customer(first_name, surname, customer_phone)
ON DELETE CASCADE
ON UPDATE CASCADE)