OutputDebugString is masked by default in Windows 7, so the message will not show in the windbg kernel session of a Windows 7 machine. To enable it, add a registry key DebugPrint under HKLM\System\CurrentControlSet\Control\Session Manager of the debuggee, create a DWORD value of 0xf named Default under the DebugPrint key, restart debuggee, the OutputDebugString message will be seen in the debugger.