CUDA 6 installation error in Windows 8.1

Hi all
My system is i7, 16 GB with GTX630 installed. Cuda 5 worked but 6 installation failed. I have removed 5 and re-install 6, but same error. There is no clue of what happened but it just bombed at Cuda toolkit all the time. I extracted the files into a temp dir and use command line setup ( got it from this mailing list as well) and following is the lone error from the log.

ERROR: [NVI2.NVInstaller] 235@CNVInstaller::PerformSteps : Installation failed with error Exception {0x8007010b - The directory name is invalid.; File: SimpleThread.h; Line: 228}.

Any gives?
thanks in advance

Just to add, mine is windows 8.1, 64 bit. I have VS2012 and VS2013 installed. I tried installing nsight by using separate installer comes with CUDA 6 - and it installed without problem. The issue is in CUDA 6 toolkit installation.