Attempt to invoke directory as script
This occurs when Apache is configured with ScriptAlias or SetHandler and a request is made for a directory path. The problem is that under those circumstances, all resources under a certain path are considered to be executable.
To get around this and allow DirectoryIndex to work again, use AddHandler with Options ExecCGI, or SetHandler in a <Files> stanza.
For example, replace this:
ScriptAlias /cgi-bin /var/www/cgi-bin
Alias /cgi-bin /var/www/cgi-bin <Directory /var/www/cgi-bin> AddHandler cgi-script cgi pl Options ExecCGI </Directory>