Insert Javascript advert into sidebar

I have an affiliate account with a currency exchange company. They provide me with javascript code to insert into my websites. It calls on their site to download the .js file.
When trying to insert this code into the sidebar using BLANK WIDGET it screws up the site. It prevents the footer from being displayed and also when a user clicks on login, the login form is prevented from being displayed. And the image is not displayed either. Any ideas? Thanks.