Ok tried another test, This is what I get in the Notifications of CB Subs

12/19/2011 11:56:57 IPN payment gateway communication error ARB-Silent: mandatory param missing
12/19/2011 11:56:55 Autorecurring payment Successful. subscr_payment Completed
12/19/2011 11:56:55 Payment APPROVED web_accept Completed

What param is this? On earlier tests I was getting a ARB-Silent: ARB silent post Hash check failed. This would occur after the period had expired and a new period was supposed to begin, the rebilling. But I need to know what this initial error is first before I can test that other.

Double checked silent post URL, it matches on Authorize. I also had reset the hash prior to conducting this test, what else to look at?

I noticed on another thread it was suggested to have a 3 day grace period before the subscription actually cancels. Would that still be recommended? Since Authorize only captures the card, and processes at a later time in the day, would a CB Subscription cancel before Authorize rebilled the 2nd time or is this a non-issue?

Thanks for the help so far!

Makes sense for the initial sale, but for subsequent, 2nd, 3rd is a grace period necessary?

I wasn't sure if on the renewal of the subscription, it might cancel in CB Subs, because the payment was scheduled to process After the plan's expiration.