I am at wits end on trying to fix this issue - asio4all v2 playback timing master not connected to tascam us-1200. I have done a complete reinstall of Sonar, Asio drivers, and my Tascam US-1200 drivers, disabled the Wavetable synth, made sure no other applications were hijacking Asio, even rolled back Widows... problem persists. HELP PLEASE!

i think you dont need Asio4all with your tascam us-1200 just select asio...in driver-mode
 
 

ASIO drivers were updated for Windows 10 last year
http://tascam.com/product/us-1200/downloads/

Where do I select asio... in driver mode? I did try the Windows 10 asio driver... no luck, same issue.

For instructions put your interface and Cakewalk product in this page https://www.cakewalk.com/Support/Knowledge-Base/Audio-Hardware-Setup-Guide
 

Trying to use ASIO4ALL and the tascam drivers is probably causing problems. I would delete both and start fresh with the tascam drivers