"Object expected error" with prototype.js and IE 8

[Ignacio González Arboleya]

 I am using renderSupport.addScript() in order to add some JavaScript to my 
webpage. It works perfectly in Firefox, IE 7 and IE 8... However, although it
also works well in IE 8, you can read an error saying "object expected" 
associated with prototype.js. It only happens in IE 8.

Does anybody know anything about this issue?

Thankyou