Sonar (X2) is rock solid for me when I start it first thing.  However sometimes if I run a softsynth or other sound program first (haven't figured out a pattern but that's not the question), I get a message saying that Sonar cannot find the drivers or devices (or something like that) when I later start Sonar.
 
Rebooting the machine always resolves the problem, but it takes an annoying amount of time.  My question is this: is there something I can tell Sonar to do, some kind of device rescan for example, that can get things up and running more quickly that a full OS reboot?

How about posting your computer specs, soundcard, Windows version, Sonar version (32- or 64-bit)? Sounds like you have a bad driver. Also, can you post the exact error message? That might help us figure out which device is failing. 

Has your system gone into hibernation in between sessions ?

Depending on your soundcard/interface, a reboot is sometimes necessary to get it back, though when it's happened to me Sonar didn't complain about it.

It could be that the other synth or program is not releasing the audio driver.

See if that could be the problem. 

so, this is a guess, but sometimes with some devices, I have to turn the device off before sleeping or hibernating. Some devices handle it better. You can always try turning your interface off and back on before launching Sonar.

Also turn your interface off before leaving your PC.
 
I can say that some interfaces I have are better than others and surviving sleep events.

Logging off and logging back on is faster then re-booting and kills most open processes. I used to get hung up drivers occasionally with my old ESI Juli@ card and logging off was always enough to fix it.

In response to various posts:
 
I didn't want to turn this into a major diagnosis effort (at least initially).  I just wondered if there was some quick fix to try first (like turning off and on the interface) that was faster than rebooting (like logging off/on).  I didn't have the exact message handy because I haven't figured out how to make this happen on demand (although that probably wouldn't be too hard).  The problem is an occassional annoyance but not a show stopper.  In fact, if I just use Sonar as a synth host rather than run the standalone versions, I don't have the problem at all.
 
I agree that the culprit is most probably one or several non-CW synths and not Sonar in the first place.  Thanks for all the suggestions.

Like Glyn said. Log off then on. Annoying, but it does work and is much faster.