I've been using X3 for a few years with no problems. Today when I went to load a project, I noticed there was no sound outputting through my Scarlett 2i2 (the same device I've used for years) and there was a lag between hitting play and the project starting to play. There was no "EQ bounce" to show sound was being output either. "W" to go to the start of the recording was very laggy as well. 

When I unplugged the Scarlett, obviously I had no output but the interface returned to normal speed for playing / rewinding. Plugging in the 2i2 got the same error - no audio or MIDI output (which has worked fine for years). 

I didn't make any changes to my system, Sonar, or anything else - I did reload the driver for the 2i2, which works fine with my Windows system outside of Sonar. Any help would be greatly appreciated! I'm running Sonar X3 on  Win 8.1 system and using a Gen 1 2i2 which has worked perfectly for a long time. I tried some of the obvious driver settings, but nothing seemed to work. 

My 2i4 has also stopped working normally. Using the Focusrite ASIO driver I get a message saying that an existing project can't be played back as it is the wrong format or that another application is using the driver. I also get a message saying that the output is disabled. I've got round it for now by using the asio4all drivers. I wonder if it has anything to do with the recent major Windows 10 update. Other DAWS (FL Studio and Maschine are both working normally with the focusrite ASIO drivers, so it's Sonar-specific

Thanks for the solidarity. BTW, I was on the Digifreq forums for years, since 2001 or so - so I'm familiar with a lot of the quirks of Sonar. Were you able to use the ASIO4ALL drivers to find the 2i4 inputs? 

After a good hour with Focusrite help, I think it is the device itself. I tried 4 different drivers, disabling other drivers, updating stuff, etc. Asio4all works fine for playback, but I don't have input now. I ordered the Steinberg UR22 to see if it really is the software (I doubt it) or something with the Focusrite. I'll post here what happens. 

You certainly don't want to use asio4all in place of the focusrite driver. I tried a experiment the other day on a laptop I don't use my interface with and I have asio4all installed to use with the on board sound card.. I tried it with my Scarlett 6i6 to see what whould happen. 
It is useless as you lose most of your in and outs and the midi too. Well you guys don't have those options but it shows how bad it can be. 
Asio4all is great for on board audio-bThat is all asio4all is good for, it should never be used when a proper asio driver is available. 
Your issues are more likely not driver related and my first thoughts are USB power! 
I never recommend the 2i2 or 2i4 to people because they are buss powered. 
The Steinberg at least has the option of buss power or a wall wart. 
 
 

Some things to try:
 
Download and run "USB Oblivion", a utility that erases all traces of USB-connected drives and CD-ROMs from the registry.  Make sure to unplug any external USB drives first. (That includes the 2i2).
 
http://www.techspot.com/downloads/5629-usb-oblivion.html
 
Alternatively, you can go deeper and clean out all old, corrupt or obsolete registry entries from your system: 
With the 2i2 unplugged, uninstall the drivers, then run CCLeaner (Or any other registry cleaning utility.  I like JVPowerTools).  Reboot your system then install the 2i2 drivers per Focusrite's instructions.

Regarding ASIO4all and using the inputs on the Scarlett, this is working - I was surprised but I've recorded my guitar into Sonar using a driver that appears as ASIO4ALL v2 Scarlett 2i4 USB 1. At the moment it seems to be working so I'm tempted to leave it alone, but may try looking at the suggestions made by JonD.
 
Thing is, I believe it's a Sonar issue rather than one with the scarlett as the focusrite drivers work fine with FL Studio and with Maschine.
 
Fremont, you say ASIO4all doesn't give you inputs - I can't remember where I got my version from and I don't have the install files. I wonder if anyone else has experience of getting ASIO4all to support inputs?

I intalled Asio4all to this laptop I use at work to edit midi files. My Scarlett is at home in the studio. I brought it in and installed the drivers to see first hand what would happen. There's a lot of myths and bad information about using Asio4all on the forums. Most is possibly from old information. Asio4all is an ongoing development and improvements are made just like all software.
 
Anyhow, first they say asio4all interferes with your real ASIO driver. This was not true with the Focusrite driver and I had no problem switching between the Focusite driver and asio4all. But under Asio4all I lost my 3/4 input, my 3/4 output, SPDIF in/out and the MIDI ports. So for my interface a 6x6 + midi asio4all did not work. I will admit
 that I did not go into asio4all set up where I might have been able to make this work. I realized this later after I took the 6i6 back home. But that said I have no problem using the proper Focusrite drivers and I really believe you should have no problem either.  
 
I'm using the latest download of asio4all on a W7 64 bit laptop.  But to make this clear,,, this is on a laptop I do not have a proper interface engaged. For my DAW in the studio I absolutely would not use ASIO4all and use the proper drivers supplied by Focusrite ( and Tascam) Asio4all is only good for use with on board audio sound cards and certain brands of USB interfaces where the company failed to supply a good driver. Focusrite is not one of these companies and has good drivers, use them. If they are not working I would contact Focusrite support.  

Thanks so much for chiming in - I ended up ordering a steinberg UR22mkII and it works perfectly. I have no real idea what happened with the 2i2, but I can say it also didn't work with Pro Tools free suite or Cubase. I'd guess the problem was deep in the registry or some update that borked the compatibility. I did try clearing the USB port data, running CC Cleaner, and Focusrite talked me through some fairly technical driver replacement techniques, all to no avail. 

Being as I have the 2i2 on my hands, I'd like to sell it but I can't say for 100% if the hardware is damaged or my system just got messed up beyond (reasonable) repair. I'll add the UR22mkII is a newer interface and has some features I like and, well, it works.

Well it would be easy to test the 2i2. Just find another computer and try it out. 
But at only $140 new you'll be hard pressed to get $75 for it. 

my issue is resolved (well almost entirely)
I was intrigued by follow JonD's advice about USB ports but before using that app to clean up USB ports, I simply swapped ports. I still get a sequence of loud clicks whenever the ASIO driver initialises, but it works fine subsequently. So thanks for pointing me in the right direction. Hope I didn't hijack the OP's thread with what I thought might be a related issue. Glad you have got a working system