I recently updated my Windows computer. After that, I can not get my playback to play through my audio interface... Tascam US-1200. I have never had an issue prior.  I reinstalled everything... no success. The ASIO panel shows the Tascam US-1200 X'd out in RED and say unavailable. I have disabled the Wavetable Synth... no effect. The error message also asks if it is being used by another application, however no other applications are running. All other sound functions on the computer are working fine through the interface including Internet browsers, sound files on my computer, etc.

Sounds like something is taking exclusive rights to the sound interface not sharing. What version of the OS are you running? Microshaft are good are screwing basic things up without admitting to it.
 
I would be inclined to look at the running processes and applications also to see what is using the hardware. USB sound interfaces and not great at switching between driver modes in my experience. PCI has the added advantage of running outside the shared path of non-related hardware. 
 
It might be worth trying this. http://www.nirsoft.net/utils/usb_devices_view.html
This will let you clear up any registered port assignments, even if not necessary it's good to keep that side of things clean.
 
Check your soundcard is being shared in Sonar. Also hanging music applications can take your driver hostage with a ransom fee. 
 

Have you tried to reboot your PC ?

Did you check the Device manager to see if there is another audio option installed? if so disable the drivers for any other Audio devices.
I would remove all audio devices from the device manager and uninstall the US 1200 drivers then reboot.
go right into the device manager and see if any audio devices installed. if they did disable them and install the US 1200...
Re boot.
 

11Dreams
Did you check the Device manager to see if there is another audio option installed? if so disable the drivers for any other Audio devices.
I would remove all audio devices from the device manager and uninstall the US 1200 drivers then reboot.
go right into the device manager and see if any audio devices installed. if they did disable them and install the US 1200...
Re boot.
 

Thanks 11 Dreams... you nailed it!