Solution
The yellow warning triangle on a PXI card indicates the card has not been identified correctly, normally due to a missing or incompatible driver.
For NI timing cards like the PXI-6683H, you need the
NI-Sync driver. Check
NI Hardware and Software Operating System Compatibility for information on the driver version support for the different NI timing cards (note the excel spreadsheet attachment at the bottom of the page for a more complete table).