Installing knowledgetree getting 500 error

If you are installing knowledgetree document management software and get a 500 server misconfiguration error you likely don't have mod_expires loaded into apache.

to fix (on debian)
a2enmod expires

You can confirm that this is your problem by checking your server's error log for where it complains about ExpiresActive directive in your .htaccess file. If you find that, the above command will fix it.