I mistakenly thought the embedded OS was partly on the flash card of the PXI RT Controller (bought several years ago and since unused). In MAX, under the "Install Software" option, it has an "Update OS" button where it can update the BIOS with newer OS, but the button was greyed-out. Turns out I had a policy restriction in effect on my PC and when lifted I did update the OS (close jumper W2). All the 7.1.1 software drivers loaded fine after that. Anybody moving from RT 6.x to RT 7.x on PXI may have encountered this.
I'm no expert, but anything that prevents you from full access to the web site where the PXI OS updates are located will keep the "Update OS" button from working. Most common cause may be a firewall. Logon with administator rights. Make sure you have a minimum of 64MB flash card too. I'm using MAX 3.1.1. Last desperation move - uninstall and reinstall DAQ (7.4). Good luck.