It's not all that strange. I had this issue with my Quad Capture for over a year. Posting on the forum, contacting Roland support did not fix this issue...and given that Roland stopped updating the driver, no fixes from their end. Only work-arounds. Driver not found, close Sonar, turn off QC, and turn back on, restart Sonar and usually all good. However on a number of fairly frequent occasions, Sonar would drop it during work on a project...usually when inserting a plug-in, and I'd have to save the project, close it, turn of QC blah blah. Very unstable and frustrating.
 
The other issue was when closing Sonar, the QC driver would, on many occasions, hang on the system. I'd have to go to Task Manager and manually close it, but more often than not, it would take minutes - up to 8 - before windows released it. 
 
The only way I solved it the whole sorry process, was to buy another interface - my RME UFX. I have never had this issue of Sonar not finding the audio driver. On occasion, the driver would hang in Sonar after a crash usually, or if it's not playing with a plug-in well but going into Task Manager and manually closing it, would have windows releasing it almost straight away. 
 
My QC is now used for play back of wave/mp3's, net audio etc. 
 
The only issue I'm continuing to experience with my RME and Sonar, is that placing plug-ins on a bus, will on occasion, cause an audio loud protest/spack attack. I have to then save the project and restart and it's then all good. No-one, RME, Sonar, Noel, Forum, waves, FabFilter - not just these plug-ins...even Cakewalk plug-ins -  have solved this issue...but this is another forum topic which is pretty useless as no-one can solve it. Maybe making some negative noise about it and threatening to move to Pro Tools will get some answers? hahah. 
 
Good luck with the Quad...you're going to need it. I'm sorry I ever bought it in the first place. I hope you don't have to do buy another card, but I have not for one moment regretted buying the RME...except when an XLR plug got stuck in it...still in there.:-(
 
 
 
 
 
 

I run a VS-100 with an OctaCapture expansion.  I had multiple issues with the drivers not loading in Platinum and all of my standalone programs after a Windows update.  I did multiple uninstall/reinstalls to let Windows reload the drivers without any luck.  One program would load and work, another would not.  I'd close and reopen a program and have to start all over again.
 
I set the sample rate to 48K and did one last uninstall/reinstall of the Roland drivers.  That didn't help.  I opened the Device Manager in Windows, expanded the Sound, Video, and Game Controllers, scrolled to the VS-100 and disabled it.  Windows told me I had to reboot for the change to take effect.  I did, then went back into Device Manager and re-enabled the VS-100.  The only issue I had after that was Toontrack's EZ Mix wouldn't run standalone at 48K.  I've since found out that EZ Mix will only run at 44.1 in standalone.
 
It's been a couple months and the drivers are still holding.  I have no idea why disabling and re-enabling the VS-100 in Device Manager worked when everything else failed.  I'm pretty happy it did, because I was at the point of pricing out other soundcards.  Hopefully, this might help someone who is at that point.