Looks like the NI 9220 is not supported by cRIO scan mode:
It's mostly a sign of inadequate communication between the hardware and software sides of my project, but this threw a major wrench in my gears recently. I wasn't anticipating any difficulties like this because it doesn't seem like a super exotic module. Anyone know if there are plans in work to have this module supported?
Since I've seen this post referenced a few times, I would like to call out that the 9220 IS supported by Scan Mode. Please see the link in the original post as this is a living document and updated regularly.
I recently ran into this issue. To use the 9220 with cRIO Scan Mode Interface requires (minimum):
LabVIEW 2015, CompactRIO drivers August 2015, and LabView 2015 Real-Time module.
On this page, Select: C Series modules and accessories, then NI 9220.