The Global statement must be outside the procedure section of the script. Global variables are available to all functions and subroutines in your program.
Example
Global Const Height = 14.4357
Const PI = 3.14159 ' Global to all procedures in a module.
Sub Main()
Begin Dialog DialogName1 60, 60, 160,70, "ASC - Hello"
TEXT 10, 10, 100, 20, "Please fill in the radius of circle x"
TEXT 10, 40, 28, 12, "Radius"
TEXTBOX 42, 40, 28, 12, .Radius
OKBUTTON 42, 54,40, 12
End Dialog
Dim Dlg1 As DialogName1
Dialog Dlg1
CylArea = Height * (Dlg1.Radius * Dlg1.Radius) * PI
MsgBox "The volume of Cylinder x is " & CylArea
End Sub