Update for those who are curious (I'm always interested in how these things pan out): Turns out it was the fact that we had a 60 month amortization schedule on one line of this vendor bill, and NetSuite didn't like the fact that we only had 3 more years of accounting periods created, not 5. Created periods through 2030 and was able to manually push the bill through. Will have to go back and adjust the workflow to account for this edge case and maybe throw some sort of message/error in the UI, but that's a project for later in the year when things free up (haha).