I’m getting the following javascript error when going to the checkout page:

Line: 83

Char: 1

Error: ‘Sys.WebForms.PageRequestManager’ is null or not an object

Code: 0
URL: https://myprincessacademy.americommerce.com/store/OnePageCheckout.aspx

I'm using IE7 as the browser running on Windows Vista.  Please advise...