After updating a really old transaction key on our fully patched Magento 1.9.3.2 site where everything was working fine, I uploaded a series of 4 new transaction keys, disabling the previous ones immediately, and tested on both our website and through Live Console on the Developer.Authorize.Net site. All of them failed with the same message "Gateway error: The merchant login ID or password is invalid or the account is inactive." on our production site and with the E00007 error on the Live Console.
Our original API urls were https://secure2.authorize.net/gateway/transact.dll and https://api2.authorize.net/xml/v1/request.api and I have tried all iterations of these urls leaving off the 2 and nothing works. Site is not in test mode.
The new sandbox keys for our dev site seem to work fine in both our test site and in the Sandbox Console, but this is not a production site.
I have compared the Magento Paygate files with the git versions and all match. I have also changed the RESPONSE_DELIM_CHAR from (~) to (*) because there was some indication on the internet that this might be a problem. It made no difference. Any other thoughts?