Issues with Inputbox

Hi,
Sorry im really new to this, but i keep getting this message popping up every time i try to run this script, iv been trying for a while to work out whats going on, but i cant.


#include <ButtonConstants.au3>
#include <EditConstants.au3>
#include <GUIConstantsEx.au3>
#include <StaticConstants.au3>
#include <WindowsConstants.au3>
#Region ### START Koda GUI section ### Form=
$Form1 = GUICreate("What is Needed", 655, 262, 503, 181)
GUISetBkColor(0x99B4D1)
$Input1 = GUICtrlCreateInput("", 48, 112, 209, 21)
$Input2 = GUICtrlCreateInput("", 384, 112, 209, 21)
$Input3 = GUICtrlCreateInput("", 48, 200, 209, 21)
$Label1 = GUICtrlCreateLabel("What is needed in an Exam to Obtain a Certain Grade", 16, 8, 623, 33, $SS_SUNKEN)
GUICtrlSetFont(-1, 18, 800, 0, "MS Sans Serif")
GUICtrlSetBkColor(-1, 0xC0DCC0)
$Label2 = GUICtrlCreateLabel("Insert Essay Percentage obtained here:", 40, 96, 228, 17)
GUICtrlSetFont(-1, 8, 800, 0, "MS Sans Serif")
$Label3 = GUICtrlCreateLabel("Insert Intended Final Grade here:", 56, 184, 192, 17)
GUICtrlSetFont(-1, 8, 800, 0, "MS Sans Serif")
$Label4 = GUICtrlCreateLabel("Insert the Percentage of the total ", 392, 80, 197, 17)
GUICtrlSetFont(-1, 8, 800, 0, "MS Sans Serif")
$Label5 = GUICtrlCreateLabel("mark which the essay counts for::", 392, 96, 195, 17)
GUICtrlSetFont(-1, 8, 800, 0, "MS Sans Serif")
$Button1 = GUICtrlCreateButton("Calculate", 376, 176, 225, 49)
GUICtrlSetFont(-1, 8, 800, 0, "MS Sans Serif")
GUISetState(@SW_SHOW)
#EndRegion ### END Koda GUI section ###


While 1
$nMsg = GUIGetMsg()
Switch $nMsg
Case $GUI_EVENT_CLOSE
Exit

$essay_perc2 = guictrlread($Input2)
$essay_perc1 = ($essay_perc2 * 0.001)
$Exam_perc = (1 - $essay_perc1)
$essay_count = guictrlread($Input1)
$Final = guictrlread($Input3)
$ans = ($essay_count * $essay_perc1)
$ans1 = ($Final - $ans)
$ans2 = ($ans1/$Exam_perc)

Case $Button1
MsgBox (4096, "Answer", $ans2)
Exit

EndSwitch
WEnd


any help would be amazing
thanks