I am afraid that is not how you fix that issue. The reason you received that error is because the "Program Files" part of your path had a space. Thus the shell assumed that the path you were using was "C:\Program" and not "C:\Program Files\Microsoft SDKs\Windows\v6.0A\bin\gacutil.exe" That is why I put "C:\Program Files\Microsoft SDKs\Windows\v6.0A\bin\gacutil.exe" in quotes above. I am afraid entering the command as you did in your first(the question) post would still yield the same error.