Classic Sonar / Sound Card Error - Need Help

***  See updates at bottom of this initial entry ***
 
Guys,
 
I am at the very end of a massive XP DAW rebuild project and just when I thought I was finished I got the classic error: "The default audio is not compatible with one or more soundcards" when I tried setting the bit depth to 24 bit.

My main audio device is a Fireface 400.  But I also have a Realtek on-board sound card that I do NOT want to disable, and AFAIK I should be able to leave it enabled as long as it is not referenced inside Sonar settings.  During my test builds I don't recall this being any problem.  And I know for a fact it was never a problem previously when I used a 16 bit SBLive card as my secondary card either.  (I need a secondary system audio card for my work flow outside of Sonar, so please do not recommend that I just disable the device as that isn't an option)
 
Any guidance on what might be going on, what to look for, or adjust??
 
Sonic
 
*** Update ***
I "fixed" the problem I THINK but I still would really value any input from the great people on the forum.  It seems the problem was the FF400 was set in Sonar for 3 bits instead of 32 bit PCM left justified.  HOW in the heck this happened I have no clue, it never did this before, and it didn't do this on the DAW rebuild test-runs I did.   I'm not feeling too confident about this very bizarre finding, even though it seems to be the resolution. 
 
*** Update #2 ***
So upon reflection I think I know what happened. Apparently in Sonar 2 I did not change the Driver Mode setting when I tried to convert from on-board sound card to the RME and instead it was left as "Default" (or something to that effect).  So when I profiled it was probably using the MME driver and that's why the Sonar set the RME as 3 bit instead of 32 bit PCM left justified.  That in turn then caused Sonar to fail on the 24 bit setting as well.  After which I went into Sonar 5 and tried, but had WDM/KS set correctly, however it too ended up then erroring upon profile.  Which leads me to believe somehow this sequence got things twisted up between the OS and the two Sonar versions.  I was always under the impression each Sonar version was it's own entity that didn't impact another version.  Apparently this must not be the case in all instances.  Because uplugging the RME Fireface, rebooting, re-starting Sonar, and then pluggin the RME back in, rebooting again and re-profiling in Sonar seemed to iron all this out in both Sonar 2 and Sonar 5.   I'm baffled, would really like to understand more about this behavior I encountered, can't help but believe there's a some important nuances to be learned.

Sonar 5?  Windows XP? 
Time to upgrade....

Wow.  Thanks.  That insight is staggeringly helpful.  <grin>
 
Well....I parceled apart the problem.  Unplugged the RME and tried using just the onboard sound card in Sonar (since I know that worked before while testing prior rebuilds). Sure enough it worked.  So I plugged the RME back in, re-adjusted Sonar's settings and re-profiled, and this time everything worked as it should have.   I then recalled Sonar behaved rather strangely during the test-builds about this same phase as I was trying to set up the RME in Sonar following driver installation. I have no idea where the conflict is but the short answer is that with a bit of prodding Sonar and the OS things seems to eventually iron out.
 
If any of you guys have any tips or insight into what might be going on or how to minimize this type of issue in the future please let me know.  I annotated what happened and next time will probably try to make the necessary Sonar Audio settings/adjustments in small steps rather than all at once.   It may be that since Sonar initially defaults to the on-board sound card, when I later install the RME maybe it causes Sonar to freak out unpredictably if I perform the many Audio adjustments/settings all at once.  Not to mention there is more than one Sonar version involved and they were set to different driver modes by accident this time. So maybe those profiling processes got the OS confused in some way.  The only error in a lengthy effort to build this DAW, so I sure hope it ironed itself out and isn't going to become a persistent Gremlin....
 
Sonic

Another update:

So upon reflection I think I know what happened. Apparently in Sonar 2 I did not change the Driver Mode setting when I tried to convert from on-board sound card to the RME and instead it was left as "Default" (or something to that effect).  So when I profiled it was probably using the MME driver (and that's why the Sonar set the RME as 3 bit instead of 32 bit PCM left justified).  That in turn then caused Sonar to fail on the 24 bit setting as well.  After which I went into Sonar 5 - which had WDM/KS set correctly, however it too ended up then erroring upon profiling.  Which leads me to believe somehow this sequence got things twisted up between the OS and the two Sonar versions.  I was always under the impression each Sonar version was it's own entity that didn't impact another version.  Apparently this must not be the case in all instances.  Because by unplugging the RME Fireface, rebooting, re-starting Sonar, and then pluggin the RME back in, rebooting again and re-profiling seemed to iron all things out in both Sonar 2 and Sonar 5.   I'm really baffled, would really like to understand more about this behavior I encountered, can't help but believe there's a some important nuances to be learned.