error C1190: managed targeted code requires a '/clr' option - c++

Question

Found a lot on this error already, but my case does not get matched with any yet.
I am building a solution (having many projects) in debug mode, and one of them is throwing this error, I am using VS2010 and language is C++, .net version 4.0, earlier this project was compiled in vs2008 and then VS2010, and it was all ok, now I got a new machine which has just VS2010 installed and now facing this error.
Main thing to notice is:
Properties settings:
Project Configuration->General->/CLR is chosen
In C++->General-> No CLR support
I am having these settings since past, it's running all fine in my old machine in VS2010 only in the same debug mode.
What to do?

Answer 1

I am using Visual Studio 2013.
I had similar symptoms for a very simple C program. In the project properties I changed the General / Platform-Toolset setting from "Visual Studio 2010" to "Visual Studio 2013 v120" and that got rid of this error for me.

Answer 2

As the error indicates, precompiled headers are not compatible with /clr-compiled files.
You can disable precompiled headers for the cpp files that are compiled with /clr or for the whole project (C/C++ -> Precompiled Headers -> Precompiled Header : Not Using Precompiled Headers). I'm not sure what the difference is but both seem to work for me.

Answer 3

Doc is not exactly wrong, but I'm betting that's not what's going on here.
Do you by any chance have something like THIS:
#using namespace boost::asio;
...instead of something like THIS?
using namespace boost::asio;
Both "using" and "#using" have valid roles in Visual Studio-- but if you mean the pure C++ language keyword, be sure you are using the former! The latter is indeed used for managed code. See here:
https://msdn.microsoft.com/en-us/library/yab9swk4.aspx
Getting this wrong in Visual Studio 2015 has the following effects:
BUILD OUTPUT:
1>thingy.cpp(3): error C2006: '#using': expected a filename, found 'namespace'
1>thingy.cpp(3): fatal error C1190: managed targeted code requires a '/clr' option
Note that attempting to "satisfy" this in a fit of 4:00 AM frustration by removing the "namespace" keyword and quoting the value will result in only the second error.
(I think that's worth mentioning, because as both Visual Studio and the C++ language specification continue to change, people try all kinds of syntax that they know shouldn't work, and if it suddenly compiles, just assume the spec or the tools have changed in some way they haven't had time to keep up with-- especially if the error messages seem to have something to do with "features" they couldn't care less about, and don't use.)