[ZPatterns] what I'm doing wrong? (random errors)

[Antonio Beamud Montero]

Hello again:
I have a little problem. Al my system works well, but after some time
working with it, fails.

I have a Folder, and inside, different objects (plugins). Some of this
objects contains a list of references to objects contained in the same
folder. 
When I try list that references using:

<dtml-in list_plugins>
  <p><a href="<dtml-var absolute_url>"><dtml-var id></a>
</dtml-in>

When I click in this generated links, all works well, but some time
later when I try to click in it, Zope return me the next error:

Error Type: AttributeError
Error Value: get


 File
/usr/local/Zope-2.4.1-linux2-x86/lib/python/Shared/DC/Scripts/Bindings.py, line 354, in _bindAndExec
    (Object: editMachine)
  File /usr/local/Zope-2.4.1-linux2-x86/lib/python/App/special_dtml.py,
line 244, in _exec
    (Object: editMachine)
  File
/usr/local/Zope-2.4.1-linux2-x86/lib/python/DocumentTemplate/DT_In.py,
line 770, in renderwob
    (Object: list_installed_plugs)
  File /usr/local/Zope-2.4.1-linux2-x86/lib/python/OFS/Traversable.py,
line 107, in absolute_url
    (Object: PlugInBase)


I'm using PlugIns Product and all this objects are plugins. How I can
debug this problem. Anybody has any idea? Why all works well during a
moment..?

Thanks