[Zope] Help for duplicate key (?) error

[Zanotti Michele]

Hi all,
Excuse if this is a trivial problem. I have Zope 2.5 on NT 4.0. When I'm
working on an object in ZMI and click on the view tab I have a Key error.
If I open a new window browser (IE6) I can work regularly, but after some
time I have this error again. Thanks to anyone can explain this error to me.
This is the traceback: 
Traceback (innermost last):
  File D:\PROGRA~1\ZOPHEL~2\lib\python\ZPublisher\Publish.py, line 150, in
publish_module
  File D:\PROGRA~1\ZOPHEL~2\lib\python\ZPublisher\Publish.py, line 114, in
publish
  File D:\PROGRA~1\ZOPHEL~2\lib\python\Zope\__init__.py, line 158, in
zpublisher_exception_hook
    (Object: dl_DirezionePersonale)
  File D:\PROGRA~1\ZOPHEL~2\lib\python\ZPublisher\Publish.py, line 98, in
publish
  File D:\PROGRA~1\ZOPHEL~2\lib\python\ZPublisher\mapply.py, line 88, in
mapply
    (Object: advanced_search_form)
  File D:\PROGRA~1\ZOPHEL~2\lib\python\ZPublisher\Publish.py, line 39, in
call_object
    (Object: advanced_search_form)
  File D:\PROGRA~1\ZOPHEL~2\lib\python\OFS\DTMLMethod.py, line 127, in
__call__
    (Object: advanced_search_form)
  File D:\PROGRA~1\ZOPHEL~2\lib\python\DocumentTemplate\DT_String.py, line
473, in __call__
    (Object: advanced_search_form)
  File D:\PROGRA~1\ZOPHEL~2\lib\python\OFS\DTMLMethod.py, line 120, in
__call__
    (Object: standard_html_header)
  File D:\PROGRA~1\ZOPHEL~2\lib\python\DocumentTemplate\DT_String.py, line
473, in __call__
    (Object: standard_html_header)
  File D:\PROGRA~1\ZOPHEL~2\lib\python\DocumentTemplate\DT_Util.py, line
159, in eval
    (Object: zss_root.style())
    (Info: zss_root)
  File <string>, line 2, in f
  File D:\PROGRA~1\ZOPHEL~1\lib\python\Products\ZStyleSheet\ZStyleSheet.py,
line 249, in style
    (Object: zss_root)
  File D:\PROGRA~1\ZOPHEL~1\lib\python\Products\ZStyleSheet\ZStyleSheet.py,
line 210, in _value
    (Object: zss_root)
  File D:\PROGRA~1\ZOPHEL~1\lib\python\Products\ZStyleSheet\ZStyleSheet.py,
line 203, in _children
    (Object: zss_root)
  File D:\PROGRA~1\ZOPHEL~1\lib\python\Products\ZStyleSheet\ZSSRule.py, line
170, in _value
    (Object: Td_d_contents)
  File D:\PROGRA~1\ZOPHEL~1\lib\python\Products\ZStyleSheet\ZSSRule.py, line
162, in _children
    (Object: Td_d_contents)
  File D:\PROGRA~1\ZOPHEL~1\lib\python\Products\ZStyleSheet\ZSSAttribute.py,
line 82, in _value
    (Object: border-right)
  File D:\PROGRA~1\ZOPHEL~2\lib\python\DocumentTemplate\DT_String.py, line
273, in __init__
  File D:\PROGRA~1\ZOPHEL~2\lib\python\DocumentTemplate\DT_String.py, line
349, in initvars
  File D:\PROGRA~1\ZOPHEL~2\lib\python\ZPublisher\HTTPRequest.py, line 845,
in __getitem__
  File D:\PROGRA~1\ZOPHEL~2\lib\python\ZPublisher\HTTPRequest.py, line 837,
in get
  File
D:\PROGRA~1\ZOPHEL~2\lib\python\Products\Sessions\SessionDataManager.py,
line 91, in getSessionData
    (Object: session_data_manager)
  File
D:\PROGRA~1\ZOPHEL~2\lib\python\Products\Sessions\SessionDataManager.py,
line 174, in _getSessionDataObject
    (Object: session_data_manager)
  File D:\PROGRA~1\ZOPHEL~2\lib\python\Products\Transience\Transience.py,
line 133, in new_or_existing
    (Object: session_data)
  File D:\PROGRA~1\ZOPHEL~2\lib\python\Products\Transience\Transience.py,
line 159, in new
    (Object: session_data)
KeyError: duplicate key 38979001A0LXI.UStIA

Thanks
Michele