exdisp.h and MessageBox problem

Hi,
I do not understand why when I include the exdisp.h
header so that i can use the webbrowser control in my
application, during build, it always gives me the error
on all my MessageBox::Show statements. Errors are as
follows
C2731: 'WinMain' : function cannot be overloaded
C2653: 'MessageBoxA' : is not a class or namespace name
C2660: 'System::Windows::Forms::Control::Show' : function
does not take 4 parameters
C2653: 'MessageBoxA' : is not a class or namespace name
C2660: 'System::Windows::Forms::Control::Show' : function
does not take 4 parameters

Am I doing the right thing or is there anything i must do
to access the webbrowser control when creating a managed
c++ application?
Email: (E-Mail Removed)

Regards
Joyce