unregistered xsl code: page2html.xsl

Traceback (most recent call last):
  File "/vls/instance/server/dynamic/vls/wiki/utils.py", line 219, in renderWikiPage
    return vl.customxslt.convertRootWithXslt(root, 'page2html.xsl', ddata, params=params)
  File "/vls/instance/server/dynamic/vls/wiki/__init__.py", line 1163, in convertRootWithXslt
    xsl_file, xsl_dname, debug_write = self.prepareXslt(ident, ddata, logger=_log)
  File "/vls/instance/server/dynamic/vls/wiki/__init__.py", line 1109, in prepareXslt
    ident=ident, domain=ddata, with_updatets=True, resolve_unregistered=resolve_unregistered)
  File "/vls/instance/server/dynamic/vls/wiki/__init__.py", line 1201, in getXslWikiCode
    raise UnregisteredXSLError('unregistered xsl code: %s' % ident)
UnregisteredXSLError: unregistered xsl code: page2html.xsl