Reference to Form1 in Form5

[Jennifer84]

I have 2 Forms like this. What I do with the codes below is to press a button on Form1.
When doing this, button1 on Form5 will activates. This works perfect.
I use this code:

Inside Form5:

public: System::Void PressThisButton()
{
   button1_Click(this, EventArgs::Empty);		 
}

Inside Form1:

#include "Form5.h"

//Declaring a reference to Form5:
private: Form5 ^myForm5; 

//Pressing this Button will activate button1 on Form5
private: System::Void button1_Click(System::Object^  sender, System::EventArgs^  e) 
{
    myForm5->PressThisButton();
}

...................................

The problem comes when I do the excatly opposite. I will press a button on Form5 to activate a button on Form1 like this below.
I tried to only #include "Form1.h" in Form5 and this gave a compileerror.
To mention is that Form1 is my "starting Form" so I wonder why this is happening.

Inside Form1:

public: System::Void PressThisButton()
{
   button1_Click(this, EventArgs::Empty);		 
}

Inside Form5:

#include "Form1.h" //This gives compileErrors ?

//Declaring a reference to Form1:
private: Form1 ^myForm1; 

//Pressing this Button will activate button1 on Form1
private: System::Void button1_Click(System::Object^  sender, System::EventArgs^  e) 
{
    myForm1->PressThisButton();
}