from mechanize import Browser

url_root = 'http://www.xxx.ru/'
username = 'xxx'
userpass = 'yyy'

br = Browser()
br.set_handle_robots(False)

br.open(url_root)

br.select_form(nr=2)
br["login"] = username
br["password"] = userpass
br.submit()

br.follow_link(text='xxx', nr=0)
#print rs.read()
rs = br.follow_link(text='yyy', nr=0)

print rs.read() # << здесь все хорошо, html выводится

br.select_form(nr=0) # << а вот тут ошибка:

"Traceback (most recent call last):
  File "./mailc.py", line 35, in <module>
    br.select_form(nr=0)
  File "/usr/lib/python2.5/site-packages/mechanize/_mechanize.py", line 492, in select_form
    for form in self.forms():
  File "/usr/lib/python2.5/site-packages/mechanize/_mechanize.py", line 414, in forms
    return self._factory.forms()
  File "/usr/lib/python2.5/site-packages/mechanize/_html.py", line 534, in forms
    self._forms_factory.forms())
  File "/usr/lib/python2.5/site-packages/mechanize/_html.py", line 226, in forms
    raise ParseError(exc)
"