To the original poster:
Your computer specs are not listed in your form profile's Signature section (see the bottom of mine for an example), so I don't know if you are running Sonar on a desktop computer or on a laptop.
IF you are running Sonar on a laptop - please try turning off or disabling your Wi-Fi adapter just prior to launching Sonar. IF this fixes things for you, then you will want to make sure that every time you are going to work in Sonar, that you temporarily turn off or disable the Wi-Fi adapter for the laptop, then launch Sonar, then when finished with Sonar turn the Wi-Fi back on or enable it, to get the internet back again. For many laptops, the presence of a Wi-Fi adapter can cause problems with Sonar.
If the above does not fix anything, or you are using a desktop computer, then please review and respond to the following:
1. Are you running a dedicated audio interface? If so, what is the model name?
2. In Sonar, are you using a driver mode of ASIO? (Edit>Preferences>Audio>Playback and Recording)
3. In Sonar, please post the Sample Rate and the listed reported latency values (Edit>Preferences>Audio>Driver Settings for both)
4. Does your project have any loaded effects? If so, please post all the plugins loaded into the particular project that is giving you the lag. In addition, does the lag go away if you hit the letter 'E' on your computer keyboard and then try to play notes on your controller? (The letter 'E' toggles on/off the bypass of all loaded effects, so if the lag goes away after bypassing all the loaded effects, then it means that one or more of your loaded effects are contributing/causing the lag. Hit 'E' again to turn all effects back on again, by the way).
Bob Bone