The error message seems quite self-explanatory. The compiler command line options /ZI and /clr can't be used together. Did you read the documentation for that error: https://msdn.microsoft.com/en-us/library/t0cs92zx.aspx
How are you trying to compile your program?
If you're using Visual Stdio, what is the exact version?
What type of program are you trying to write C++, C, C++/CLI, C#, etc.
How did you create your project? This error message is usually caused by selecting incompatible project options. For a C++ program you probably need to select a Win32 console application and make sure you don't select anything to do with .NET or CLI.
The above is only a guess since I don't use that compiler and I don't do Windows.
That means that you're not trying to write a standard C++ program because the "System namespace" is not part of the C++ standard. It is part of one of the .NET languages, like C# or C++/CLI.