Internal error message
You can see if it is installed or not by looking at the page Special:Version on your wiki.
Look in the file LocalSettings.php for a line that looks something like
require_once( "$IP/extensions/ConfirmEdit/ConfirmEdit.php" ). Try deleting the line, and see if it makes your error go away (Try this for all the extensions you have installed. However make back ups of LocalSettings.php first).
The actual extension is probably installed in mywikifolder/extensions/ConfirmEdit. You may want to try downloading a new version from extension:ConfirmEdit.