Please don't share keys nor part of keys in public forums! That's personal sensitive information. We edited your original post to remove this information.
Your key should work both on your production environment and test server, please double check whether the Web.config file in the test server has the correct key typed just like the production one.
If you lost your key or have any question that you feel like you need to double-check it, please mail us at firstname.lastname@example.org
so we can handle it better with you.
Hope this helps!
EDIT: double check your application publish process is not overwriting your test server's Web.config with a version without the key. also check if the extnet
tag is not used different times in the same Web.config file, and also add some random text to the file (so it breaks) and check if it is really the Web.config your website is using!..