"RpcAsync.h" header file not being read, in which I have put in order for recognizing AnsiString in Microsoft Visual Studio

This is my first time working with header files, and I have a source code and I'm trying to include RpcAsync.h file and written in the beginning of my source file however visual studio is not recognizing the header file for AnsiString. I am able to see AnsiString definitions in RpcASync.h .

It throws an error saying : 1 IntelliSense: identifier "AnsiString" is undefined.

Thank you