how to log for a build game freeze error

Hi there all! My game is freezing after 2-3 minute playing on build version not in unity3d editor. I profiled it by Autoconnect profiler but in exact freeze frame profiler will no longer profile the game. this problem came to me from last month and I have lots of changes. before my Unity3d was 4.2 and from last two month ago I changed my unity to 4.6.2. how can I find what cause this freeze error in my built version? I had some freezing error in my built game and because it was at certain point(in collision with some NPCs) I figured it out.but now it is randomly freeze in anywhere in game. my game is racing and for PC.