InvalidCommandAuthDigestFile

Invalid command 'AuthDigestFile', perhaps misspelled or defined by a module not included in the server configuration

This error message is likely to appear, if you are using Apache 2.2, and are still using AuthDigestFile in your config file.（如果你使用apache2.2，并且使用AuthDigestFile在你的配置文件中，这个错误的信息你就很可能看到）
You should be using AuthUserFile instead.（你因该用AuthUserFile替代它） This only applies if you are using Apache 2.2.

For example:

<Location /private/> AuthType Digest AuthName "private area" AuthDigestDomain /private/ http://mirror.my.dom/private2/ AuthDigestProvider file AuthUserFile /web/auth/.digest_pw Require valid-user </Location>