Mod_python error: "PythonHandler cldispatcher"

Traceback (most recent call last):

  File "/usr/lib/python2.4/site-packages/mod_python/apache.py", line 299, in HandlerDispatch
    result = object(req)

  File "/home/httpd/galleriacontinua.com/cldispatcher.py", line 83, in handler
    return handlerfunc(req)

  File "/home/httpd/galleriacontinua.com/src/artista.py", line 147, in handler
    req.write(HTMLResource(req).run())

  File "/usr/lib/python2.4/site-packages/sgutility2/web.py", line 136, in run
    return booundM()

  File "/home/httpd/galleriacontinua.com/src/artista.py", line 75, in GET
    assert(len(artisti)==1)

AssertionError