Foreign keys

[RuiSMonteiro]

Hello there,
 
I have a table that with a TEXT filed as a primary key.
 
I can't make a foreign key of this field on another table, why does this happens?
 
Ex:
 
Product ---
| ref - text, PK
| name - text
| ....
 
ProductsList
| ID int, PK
| profref - foreign key of the table product
| ....
 
 
Thanks for the help