Pat K

Update: it’s not the plugin – it’s a memory problem.

I was able to install wp-e-commerce only after doing each of the following (I tried this MANY different ways before getting it to work):
1) create a file called php.ini (using a text editor) and adding the following:

;; set memory limit for cache.php
memory_limit = 128M

…upload (FTP or cPanel File Manager) the php.ini file in 3 places;
– above the root directory
– in the root directory (public_html or www)
– and in the wp-includes directory

2) Add the following line below the opening <?php tag in the file wp-includes/cache.php:
ini_set('memory_limit','128M'); // set memory to prevent fatal errors

(…yes it’s modifying a core file, but it works!…just make a note of the modification)

After that, create an htaccess file for the wp-includes directory and insert the following directive:

3) Use a text editor to create a .htaccess file and add the following:

# set memory limit for cache.php
php_value memory_limit 128M

…upload the .htaccess file to the wp-includes directory.

Log out of admin, clear browser cache, login and install the module.

See the following for details:
http://perishablepress.com/press/2008/02/17/wordpress-error-fix-increase-php-memory-for-cachephp/

I hope this helps…