OK, I think I see my issue. When I initialized my device, I was setting the vbw to be what the rbw was. I then changed the rbw and kicked things off. The vbw wasn’t getting updated, so when I set the SweepCoupling to use the new rbw (200kHz now), but had the old vbw (100kHz), it caused the allocation error.
Dumb question, How do I know if I am using the 32b API or not? I haven’t seen this distinction anywhere.