I know my asio driver are installed correctly as they work in Acid, but when I go to the audio preferences in Vegas there's no option to use them. Anyway one know why?
Check the Windows Task Manager to see if ACID or another instance of Vegas is still running in memory. I have had issues where I close either ACID or Vegas but it hangs around in memory and I don't notice it until I open it again and my ASIO drivers are gone because the previous (and still running) instance has them locked.