ARB-Silent: mandatory param missing

We had 8 transactions settle in Authorize.net last night and out of the 8, 4 appeared properly in notifications and then there were 6 rows of ARB-Silent: mandatory param missing. 2 of the 8 transactions were refunds so I'm guess that 2 of the errors were for those. However there were 2 subscribers who didn't show up under notifications that were paid transactions in Authorize.net which I'm guessing were the other 4 errors. Can you help me determine why 2 of the 6 payments did not silently post?

If I need to send you login credentials please let me know.

Thanks,
Linda

An ARB is sent for single-payments and recurring-payments from Authorize.net. We only accept recurring ARB posts and the others will error with that message. We however overlooked this fact and just caused the notification to error instead of ignoring it. As long as those that failed are NOT recurring payments being received you've nothing to worry about as all other methods are validated using their API from your site to Authorize.net and don't rely on the notification.