Best method to uninstall is to reverse the install process, as explained in the INSTALLATION document bundled with the mod. This would include re-uploading the backed up Zen Cart files which were overwritten during the mod installation.
BEFORE YOU PROCEED BACKUP BOTH YOUR SHOP DIRECTORY AND YOUR DATABASE.
You don't state the version number of the mod installed. Open the readme for that version and figure out which Zen Cart files had to be overwritten/edited during the mod installation. Probably two or three template files and /admin/orders.php. Then the other Google Checkout mod files you can just delete from the server. You should only delete the mod files AFTER uninstalling the mod via (Admin > Modules > Payment Methods.
It appears the errors you report are a result of removing some of the Google Checkout mod files but not removing others. Specifically it appears you have not re-uploaded a backed up copy of the original /admin/orders.php. If you have the backup file on your hard drive then upload/overwrite the same file on the server. If not then open the the Zen Cart zip archive (for whichever version Zen Cart you are using), extract orders.php and upload to /admin/orders/php on the server (this is assuming you made no other modifications to orders.php. In that case you should do a compare and merge).
And be sure to overwrite the mod template files in YOUR_TEMPLATE directory (again apply compare and merge if you customized the original core files). If you did not previously edit/customize the relevant template files, you can just remove those from your YOUR_TEMPLATE directory (no need to upload the originals).
The two tables created by Google Checkout 1.3RC2 mod install, are as follows.
TABLE: google_checkout
customers_id
buyers_id
TABLE: google_orders
orders_id
google_order_number
order_amount
By default, the two tables are NOT removed when you uninstall the mod (Admin >Modules > Payment Methods). But if you are VERY certain you want to delete (drop) those two tables then there are two lines of code near the bottom of /includes/modules/payment/googlecheckout.php, which you can comment out BEFORE uninstalling the mod. Or you can just drop the two tables via phpmyadmin. BACKUP your database BEFORE you do this.
If you have used the mod in LIVE Live production to process real orders, then I do NOT suggest removing those two tables unless you are VERY certain of the the ramifications. If you have only used Google Checkout in the sandbox testing environment then there should be no issue with dropping the two tables. But I have not tested removing the tables so I am not certain. Hopefully ropu can provide clarification on this important issue.
When you state you did not know SSL was required for Google Checkout, I ask which payment method are you using that does not require SSL? I do not understand how you can allow submission of confidential customer info or process orders in Zen Cart without SSL, unless you are operating insecurely. Beware!
Hope this helps,
Woody
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