Does it only freeze in Sonar?
Does it freeze in every project, or just freezes in one particular project?
What is the sample rate and bit depth of the project?
What is in this project?
I would say that your Pc has met its limit and you may need to adjust some settings to fix it. ASIO, WDM, Buffers, too little ram, so on)
OR, it could be a rouge non native plugin or many instances of one plugin. Who knows as you need to be more specific about this.
CJ