An internal server error has occurred on modifying group membership

Can you send us the traceback -- the long error message?

Traceback

Traceback (most recent call last):

Module zope.publisher.publish, line 132, in publish
result = publication.callObject(request, obj)
Module zope.app.publication.zopepublication, line 207, in callObject
return mapply(ob, request.getPositionalArguments(), request)
Module zope.publisher.publish, line 107, in mapply
return debug_call(obj, args)
__traceback_info__: <security proxied schooltool.skin.flourish.zcml_content.FlourishGroupListView_groups.html instance at 0xd59556c>
Module zope.publisher.publish, line 113, in debug_call
return obj(*args)
Module schooltool.skin.flourish.page, line 71, in __call__
result = self.render(*args, **kw)
Module schooltool.skin.flourish.page, line 64, in render
return self.template(*args, **kw)
Module zope.browserpage.viewpagetemplatefile, line 83, in __call__
return self.im_func(im_self, *args, **kw)
Module zope.browserpage.viewpagetemplatefile, line 51, in __call__
sourceAnnotations=getattr(debug_flags, 'sourceAnnotations', 0),
Module zope.pagetemplate.pagetemplate, line 113, in pt_render
strictinsert=0, sourceAnnotations=sourceAnnotations)()
Module zope.tal.talinterpreter, line 271, in __call__
self.interpret(self.program)
Module zope.tal.talinterpreter, line 343, in interpret
handlers[opcode](self, args)
Module zope.tal.talinterpreter, line 533, in do_optTag_tal
self.do_optTag(stuff)
Module zope.tal.talinterpreter, line 518, in do_optTag
return self.no_tag(start, program)
Module zope.tal.talinterpreter, line 513, in no_tag
self.interpret(program)
Module zope.tal.talinterpreter, line 343, in interpret
handlers[opcode](self, args)
Module zope.tal.talinterpreter, line 742, in do_insertStructure_tal
structure = self.engine.evaluateStructure(expr)
Module zope.tales.tales, line 696, in evaluate
return expression(self)
/usr/lib/python2.7/dist-packages/schooltool/skin/flourish/templates/main.pt
Line 72, Column 8
Expression: <PathExpr standard:u'view/page_template|nothing'>
   - Names:
      {'args': (),
       'context': <schooltool.basicperson.person.BasicPerson object at 0xc10582c>,
       'default': <object object at 0xb78145f0>,
       'loop': {},
       'nothing': None,
       'options': {},
       'repeat': {},
       'request': <zc.resourcelibrary.publication.Request instance URL=http://localhost:7080/persons/manager/@@groups.html>,
       'template': <zope.browserpage.viewpagetemplatefile.ViewPageTemplateFile object at 0x98fb94c>,
       'view': <schooltool.skin.flourish.zcml_content.FlourishGroupListView_groups.html object at 0xd59556c>,
       'views': <zope.browserpage.viewpagetemplatefile.ViewMapper object at 0xd59558c>}
Module zope.tales.expressions, line 217, in __call__
return self._eval(econtext)
Module zope.tales.expressions, line 211, in _eval
return ob()
Module zope.browserpage.viewpagetemplatefile, line 83, in __call__
return self.im_func(im_self, *args, **kw)
Module zope.browserpage.viewpagetemplatefile, line 51, in __call__
sourceAnnotations=getattr(debug_flags, 'sourceAnnotations', 0),
Module zope.pagetemplate.pagetemplate, line 113, in pt_render
strictinsert=0, sourceAnnotations=sourceAnnotations)()
Module zope.tal.talinterpreter, line 271, in __call__
self.interpret(self.program)
M...