[Zope] strange error with lines property

[Heiko Stoermer]

I have a DMTL-Document with lines property.
in an external method I gather lines of text from a file, concatenate
them into a long string with '\n' as line separator and
manage_changeProperties() this string into the lines property of my
document.
now: everything works well (e.g. displaying the lines in my document),
but if I go to the documents property page in zope I get the following
error:
>Error Type: InError
>Error Value: Strings are not allowed as input to the in tag.

Traceback (innermost last):
  File /usr/lib/zope/lib/python/ZPublisher/Publish.py, line 209, in
publish_module
  File /usr/lib/zope/lib/python/ZPublisher/Publish.py, line 179, in
publish
  File /usr/lib/zope/lib/python/Zope/__init__.py, line 199, in
zpublisher_exception_hook
    (Object: l_1101_html)
  File /usr/lib/zope/lib/python/ZPublisher/Publish.py, line 165, in
publish
  File /usr/lib/zope/lib/python/ZPublisher/mapply.py, line 154, in
mapply
    (Object: manage_propertiesForm)
  File /usr/lib/zope/lib/python/ZPublisher/Publish.py, line 102, in
call_object
    (Object: manage_propertiesForm)
  File /usr/lib/zope/lib/python/App/special_dtml.py, line 120, in
__call__
    (Object: manage_propertiesForm)
  File /usr/lib/zope/lib/python/DocumentTemplate/DT_String.py, line 502,
in __call__
    (Object: manage_propertiesForm)
  File /usr/lib/zope/lib/python/DocumentTemplate/DT_In.py, line 689, in
renderwob
    (Object: propertyMap)
  File /usr/lib/zope/lib/python/DocumentTemplate/DT_In.py, line 639, in
renderwob
    (Object: getProperty(id))
InError: (see above)

Is this a known error (as I still have to use B4...) or did I do
something wrong?

thanks,
Heiko

--
Heiko Stoermer
MIG Augsburg