title: cudaGetDeviceCount returned errorUnknown code=30
body: <p>I installed CUDA 6.0 tookit on a Windows 8.1 machine and tried to run the <code>deviceQuery</code> CUDA sample. However, it returned the following error for Win32 and Win64 versions.</p>
  
  <pre><code>deviceQuery.exe Starting...
  
   CUDA Device Query (Runtime API) version (CUDART static linking)
  
  cudaGetDeviceCount returned 30
  -&gt; unknown error
  Result = FAIL
  </code></pre>
  
  <p>I installed different versions of the drivers and tried to compile the sample code from Visual Studio but the result of the execution was same.</p>
  
  <p>How can I solve this problem? Any suggestion is really welcome. </p>