Free Script Installion 500 Error

Hello,

I wanted to try the Free ver. of Amember. I downloaded the Zend version after running the tester script (see copy below).

However, when I go to mysite.com/amember/setup.php - I get the following error (even after chmd amember/ and amember/data/ to 777):

"Internal Server Error
The server encountered an internal error or misconfiguration and was unable to complete your request.

Additionally, a 404 Not Found error was encountered while trying to use an ErrorDocument to handle the request."

The tester file shows the following:

"Testing whether your system has ionCube Loader in php.ini...Failed
Testing whether your system has Zend Optimizer in php.ini...OK
Testing results:
No additional configuration required and aMember will work on your hosting using the following loading method: Zend Optimizer installed

Additional information: PHP version 4.3.11 (cgi)
OS Linux serve.xxxxxxxxxxxxx ELsmp #1 SMP Wed May 25 14:26:33 EDT 2005 i686
safe_mode Disabled
enable_dl Enabled
extension_dir ./
PHP Extensions xslt, xml, sockets, posix, mysql, mhash, mcrypt, imap, gd, ftp, curl, ctype, calendar, bcmath, zlib, Zend Optimizer
CURL binary /usr/bin/curl

Your help is appreciated as I think Amember Pro may suit my purposes.

Thanks!
Sam