I just installed the plugin for the first time and I noticed the same problem. For now, until an update comes out. I manually fixed the code to resolve the problem.
Cart not showing Empty message or 'Visit our Shop' link.
Found a double redundant function which appears to be initially doing the same thing. However, the first function overrides the second and doesn't allow the second function to execute and the second one is the function that processes the empty cart page.
Manual Edit Solution:
Not sure if your familiar with PHP, but if you want to try the current fix yourself, here it is:
1. If not already logged in, log into your website's wordpress dashboard/login page.
2. Under the 'Plugins' section, click on 'Editor'
3. Select 'WP Simple Paypal Shopping cart' under 'Select Plugin to Edit Menu'
4. You'll see a list of plugin files to edit, the file you want to edit is:
5. Once you've selected/verified that you're editing that file, scroll not too far down to find the following function:
$output = print_wp_shopping_cart();
Change it to the following code:
6. Click 'Update File' button and problem should be fixed.