I have noticed the exact same problem.
My system is similar: Intel i7/ Vista 64/ SB XFi.
I have no answer, but if there are two of us, there's gotta be a lot more out there.
Someone clever will have figured it out. Let's hope he sees this post.
I have much the same system ie, P6T deluxe v2 i7 920 chip 12 Gb Ram, sb audigy 2 zs, and did have early probs with pp trying to revert to Premiere Pro WDM sound. Just change it in Audio hardware setting of preferances to SB Audigy 2ZS [E880] and it should stay at that.
note Driver is 18.104.22.1680 from SB dont use microsofts driver.
This does not have to do anything with your soundcard or its driver. I've got this error message on professional audio systems, too. I tried M-Audio 2496 and a MOTU firewire device. All audio systems work good, but from time to time I get this asio-driver-error-message from premiere. I have to go into settings an choose asio driver again, then it works for a while until next message.
I saw the same problems on some cs3 installations so I think it must be a problem of software design.
Try to rise your asio buffers this might help a bit. What definitely helps is to choose the Adobe ASIO driver (Premiere Pro WDM Sound), doubleclick it and select your preferred sound-hardware. This could produce a little bit higher latencies but it's working.
For many, an update to their Audio driver will cure similar problems. Audio drivers are released very often, and things like Windows updates can render these obsolete instantly.
Next, many have found that the installation of ASIO4All has cleared up a lot of ASIO driver issues. Remember - you will need to set every Audio program to use it. Depending on your system, this could take a few hours, and you might forget one program, or two. When you go to use them, and the Audio in them does not work, just change that program's Audio Preferences.