Here is a easy to follow guide on how to reinstall your Shopp plugin.
1) Get a new copy of Shopp
Start by downloading a fresh copy of Shopp and any addons from your Shopp Store Account: https://shopplugin.net/store/account/
These files will likely be saved to your desktop or a downloads folder. Go ahead and find them.
2) Deactivate Shopp and Backup
Next login to your WordPress admin. Then go to Plugins and find Shopp. Click on the deactivate link.
Now login to your site with an FTP client. FileZilla is a free option (we like Transmit). Browse to the shopp plugin folder: wp-content/plugins/shopp.
Relocate the shopp folder one step above the wp-content/plugins folder and rename it. It should look something like this: wp-content/shopp_backup
3) Reinstall Shopp via WordPress Plugins
Go back to your WordPress admin. Then to Plugins –> Add New –> Upload.
Click ‘Choose File’ and browse to the location of your shopp.zip file, then click ‘Install Now’.
A few seconds later, you should see a message that the plugin was uploaded.
If you have any Shopp addons, see section 3B.
If not, you are all set. You can click on Activate to get Shopp running again.
3B) Reinstall Shopp Addons
Shopp addons, specifically shipping, gateway, and storage modules are not WordPress Plugins. You can’t upload them to through WordPress.
Locate your addon files on your computer. Then unzip them.
Upload the folders and files for shipping addons to wp-content/plugins/shopp/shipping/
Upload the folders and files for gateway addons to wp-content/plugins/shopp/gateway/
Upload the folders and files for storage addons to wp-content/plugins/shopp/storage/
Once all of your addons are uploaded, go back to your WordPress admin page and activate Shopp.
Video Screencast: Reinstall Shopp
Notes: Endicia & TaxCloud addons for Shopp are WordPress plugins. They can be reinstalled via WP-admin –> Plugins –> Add New.