There are many things that can cause Internal Server (500) errors. If you just uploaded your files, the most likely cause is that you transferred them in the wrong mode -- human readable files should be ASCII mode (translates end-of-line marks) and images and other unreadable files should be BINARY mode (nothing changed). If that wasn't the case, see http://www.catskilltech.com/freeSW/SMF/faqs/index.html#err500 for a list of more things to look at.

I'm not familiar with Webuzo (I take it that it runs OK at Lunarpages?), but it sounds like you got it sorted.

As previous posters mentioned ISE 500 errors can be caused by a number of issues. I am listing them below as reference:

1. Improper ownership of directories/files - normally the public_html should always be chown'd to username:nobody on Apache servers and everything under it should be username:username (where username stands for your cPanel username or LPCP by case)
2. Improper permissions of directories/files - since all our Linux servers run with suPHP the proper permissions that need to be set are 644 for files and 755 for folders or CGI/Perl scripts which are within the cgi-bin directory or which have Options +ExecCGI added to the .htaccess under the directory where the script is located.
3. Malware - to see if the ISE is related to malware you should always check your .htaccess or index.php files because they are the most common files that get infected and return ISE 500 if the infection breaks the site
4. Improper PHP configuration - all servers at Lunarpages have a predefined php.ini with the most common values defined for PHP so that a large majority of scripts can run with them. However since customizing the PHP values is allowed by using your own php.ini, some variables you may alter would conflict with the system and cause such errors. In order to determine if this is the case you should simply add "display_errors = On" (without quotes) within your php.ini file and the errors would be displayed on the browser which makes easy for them to be identified
5. PHP errors due to broken files, broken formatting or improper coding. These errors can also be determined by adding "display_errors = On" within your php.ini
6. Excessive memory usage - As you all know the shared environment is based upon an equal share of resources and there are certain limits. Whenever an account passes the limits it may experience ISE 500 errors due to excessive memory usage. This does not happen very often but does happen in cases of someone hotlinking your images, someone trying to spam your forms or trying to bruteforce your logins. Checking the latest visitors, Webalizer stats and RAW access logs can shed light on some issues and also the abusing traffic sources.
7. Improper Apache configuration - Just like for PHP we allow customization of the default Apache values. However whenever the values you set within your .htaccess are improper or conflict with the system setup you may experience ISE 500 errors. These can be easily discovered by checking the Error Logs from your cPanel/LPCP

If none of the above applies when you get an ISE 500 error then it either has to do with ASP/JSP if you happen to have them enabled and use them or if this is not the case either then you probably got a challange for the Lunarpages support staff in this case.