Error trying to sync multiple PXIe-449x boards with Data Acq Toolbox

I have a PXIe-1082 chassis with a PXIe-8840 controller and 5 PXIe-4499 cards. Following the example in HELP I create session and add analog voltage channels. Then when I add trigger or clock connection I get the following error:

The session does not contain any channels from 'PXI1Slot4'. Add channels from this device to the session before adding connections.

I know the channels have been added because I just added them.