I forgot to update this earlier and wanted to follow up while I'm thinking about it.
Did you update the LP40 card as well? That's the card that actually makes everything talk to each other on the 7400.
This was exactly the issue. Thankfully, I found some documentation before I left the customer site that day that mentioned the need to upgrade the LP40 when upgrading to 4.60, I think, which was the first software version to support the 20i. Updated the LP40 and all is well.
