[Zope] Keep getting this AttributeError

[Gitte Wange]

Hello,

I am going nuts here .. 

I have some code that I use in several places ... but there is one place it
won't work.

Here's a snip of the code:

<dtml-in "cart_obj.listProducts()">
 <dtml-let item="_.getitem('sequence-item')">
  <dtml-var item>
 </dtml-let>
</dtml-in>

The cart_obj is a Shopping Cart object and I have checked (by printing out
the REQUEST object on screen) that the object is set.

Now this is the error I keep on getting:

Error Type: AttributeError
Error Value: listProducts

And a snip of the traceback:
File
/usr/local/Zope-2.4.0-linux2-x86/lib/python/DocumentTemplate/DT_Util.py,
line 230, in eval
    (Object: cart_obj.listProducts())
    (Info: cart_obj)
  File &lt;string&gt;, line 2, in f
    (Object: guarded_getattr)
  File /usr/local/Zope-2.4.0-linux2-x86/lib/python/AccessControl/DTML.py,
line 101, in guarded_getattr
    (Object: process_ok)
  File
/usr/local/Zope-2.4.0-linux2-x86/lib/python/AccessControl/ZopeGuards.py,
line 109, in guarded_getattr
AttributeError: (see above)

Now I don't know what guarded_getattr is .. 

And I know that the above code works in the exact same way in another page
so ?

Any good ideas ?

TIA,
Gitte Wange