Installation of caldav module gives error:

When installing caldav (the trunk version) I get an error about a module named websrv_lib. Does anyone know if this is related to my python installation, my open erp installation or the caldav installer?

It points to the line in webdav_server.py (in caldav folder):
    from service.websrv_lib import HTTPDir,FixSendError

Hope you can help!

Traceback (most recent call last):
  File "/usr/lib/python2.5/site-packages/openerp-server/netsvc.py", line 244, in dispatch
    result = LocalService(service_name)(method, *params)
  File "/usr/lib/python2.5/site-packages/openerp-server/netsvc.py", line 73, in __call__
    return getattr(self, method)(*params)
  File "/usr/lib/python2.5/site-packages/openerp-server/service/web_services.py", line 639, in execute
    return self._execute(db, uid, wiz_id, datas, action, context)
  File "/usr/lib/python2.5/site-packages/openerp-server/service/web_services.py", line 619, in _execute
    return wiz.execute(db, uid, self.wiz_datas[wiz_id], action, context)
  File "/usr/lib/python2.5/site-packages/openerp-server/wizard/__init__.py", line 178, in execute
    res = self.execute_cr(cr, uid, data, state, context)
  File "/usr/lib/python2.5/site-packages/openerp-server/wizard/__init__.py", line 74, in execute_cr
    action_res = action(self, cr, uid, data, context)
  File "/usr/lib/python2.5/site-packages/openerp-server/addons/base/module/wizard/wizard_module_upgrade.py", line 92, in _upgrade_module
    db, pool = pooler.restart_pool(cr.dbname, update_module=True)
  File "/usr/lib/python2.5/site-packages/openerp-server/pooler.py", line 62, in restart_pool
    return get_db_and_pool(db_name, force_demo, status, update_module=update_module)
  File "/usr/lib/python2.5/site-packages/openerp-server/pooler.py", line 40, in get_db_and_pool
    addons.load_modules(db, force_demo, status, update_module)
  File "/usr/lib/python2.5/site-packages/openerp-server/addons/__init__.py", line 728, in load_modules
    r = load_module_graph(cr, graph, status, report=report)
  File "/usr/lib/python2.5/site-packages/openerp-server/addons/__init__.py", line 578, in load_module_graph
    register_class(package.name)
  File "/usr/lib/python2.5/site-packages/openerp-server/addons/__init__.py", line 406, in register_class
    zimp.load_module(m)
  File "/usr/lib/python2.5/site-packages/openerp-server/addons/caldav.zip/caldav/__init__.py", line 26, in <module>
  File "/usr/lib/python2.5/site-packages/openerp-server/addons/caldav.zip/caldav/webdav_server.py", line 32, in <module>
ImportError: No module named websrv_lib