Odd PT10 and 12 coinstall issue

This is my first experience having two versions installed. My issue is this: Whenever I boot the computer (W7x64), and attempt to load PT12 and any .ptx session, I get an error saying "current playback engine does not support sample rate of 48Khz". I discovered through trial and error that I must close PT12, open PT 10.3.3.10, load a .ptf session, exit PT10, then PT12 runs fine. I can load, edit, and close sessions, shut down PT12, restart PT12 and keep working. But if I reboot, I must first load PT10 and a session to avoid that error. My 003 rack is the only sound hardware under device manager (onboard sound is disabled in BIOS).

I've uninstalled and reinstalled each, twice, in different order. Same result.

Have I missed something obvious? Any ideas? TIA