I tried to create External Method from
start_dtml:
    <!--#call "manage_addExternalMethod('Method1','sss','login','methLoginUser')"-->
login.py: 
def methLoginUser():
        return "I dont know"
but view of start_dtml is dangerous: 
System Unavailable

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what it mean? trying to view traceback information I see:

Traceback (innermost last):
  File C:\Program Files\WebSite\lib\python\ZPublisher\Publish.py, line 877, in publish_module
  File C:\Program Files\WebSite\lib\python\ZPublisher\Publish.py, line 590, in publish
    (Info: /start_dtml)
  File C:\Program Files\WebSite\lib\python\OFS\DTMLDocument.py, line 212, in __call__
    (Object: start_dtml)
  File C:\Program Files\WebSite\lib\python\OFS\DTMLDocument.py, line 208, in __call__
    (Object: start_dtml)
  File C:\Program Files\WebSite\lib\python\DocumentTemplate\DT_String.py, line 513, in __call__
    (Object: start_dtml)
  File C:\Program Files\WebSite\lib\python\DocumentTemplate\DT_Util.py, line 266, in eval
    (Object: manage_addExternalMethod('Method1','sss','login','methLoginUser'))
  File &lt;string&gt;, line 0, in ?
  File C:\Program Files\WebSite\lib\python\Products\ExternalMethod\ExternalMethod.py, line 127, in manage_addExternalMethod
    (Object: ApplicationDefaultPermissions)
  File C:\Program Files\WebSite\lib\python\Globals.py, line 227, in __call__
    (Object: manage_main)
  File C:\Program Files\WebSite\lib\python\DocumentTemplate\DT_String.py, line 513, in __call__
    (Object: manage_main)
  File C:\Program Files\WebSite\lib\python\Globals.py, line 227, in __call__
    (Object: manage_tabs)
  File C:\Program Files\WebSite\lib\python\DocumentTemplate\DT_String.py, line 513, in __call__
    (Object: manage_tabs)
  File C:\Program Files\WebSite\lib\python\DocumentTemplate\DT_In.py, line 675, in renderwob
    (Object: manage_options)
  File C:\Program Files\WebSite\lib\python\DocumentTemplate\DT_Util.py, line 266, in eval
    (Object: _vars['PATH_INFO'][-(_.len(action)):]==action)
  File &lt;string&gt;, line 0, in ?
  File C:\Program Files\WebSite\lib\python\DocumentTemplate\DT_Util.py, line 150, in careful_getitem
KeyError: (see above)
 

What I doing wrong?