Answer

First, make sure that you used a plain text editor when making changes to the mt-config.cgi file¹, and that you uploaded it to your server in ASCII mode.

If uploading the file in the proper mode does not resolve the issue, open mt-config.cgi in a plain text editor and make sure that the only lines which do not begin with a # are those which represent valid settings. The general format of the mt-config.cgi file is that there are several lines of descriptive text, followed by the setting itself:

# If you place all of your MT files in a cgi-bin directory, you
# will need to situate the static files (docs, images, styles.css)
# elsewhere, so that the webserver will not try to execute them.
# The TROUBLESHOOTING section of the manual has more information.
#
# StaticWebPath http://www.example.com/mt/mt-static/
#

In the above example, the only line that you can safely uncomment² is the StaticWebPath line. If a comment marker (#) is missing from any of the other lines, this will cause an error.

Also, pay attention to case-sensitivity: DBhost is not the same thing as DBHost (and only the latter is the proper setting).

You can review the available settings for mt-config.cgi in the Configuration Settings section of the Users Manual.

Note that the settings in the Users Manual are applicable as of the latest version of Movable Type; so if you've checked everything else mentioned above and are still getting an error, make sure you've correctly upgraded to the latest version which is available.

¹ In versions prior to 3.2, the configuration file is named mt.cfg.

² To uncomment a setting means to remove the # from the beginning of the line where it appears.