We configured a Payment_AuthNetEcheck processor using this extension.
We were getting an System Warning for the API KEY being "unauthorized" for the test processor and only the test processor (10). The live payment processor (9) was/is working as expected and is not showing a system check.
The API Login ID, Transaction Key, Signature Key, Site URL and Recurring Payments URL settings are identical for paymentprocessor 9 and 10.
See Screenshot below:
The proposed solution is to not bother checking the test processor API KEY.