After upgrad­ing to Ubuntu Feisty, pam-based pass­word authen­tic­a­tion for Apache (2.2) didn’t work any­more. In the logs I found only some very use­less entries like

[Wed Apr 25 20:36:20 2007] [error] Internal error: pcfg_openfile()
    called with NULL filename
[Wed Apr 25 20:36:20 2007] [error] [client xxx.xxx.xxx.xxx] (9)
    Bad file descriptor: Could not open password file: (null)

After search­ing the web for a while I finally found a solu­tion which works per­fectly for me: Just dis­able all the other authen­tic­a­tion mod­ules using the fol­low­ing directive:

AuthBasicAuthoritative off