NSIS - Custom Page, problems with a droplist - nsis

Question

I have this Custom Page in my code, where there is a droplist with the available drives on the computer. When the user chooses the drive he wants, a .txt file is created where is written that drive (example: E:).
When you open the custom page, the drive that appear on the droplist is "C:\". But if I hit "next" without clicking on the droplist, the .txt file is not created. Even if I want C:\ and it's already there, I have to go there and click to make it work. If I don't click on the droplist before hiting "next", nothing happen.
Anybody knows why? The code is down below:
!include "MUI2.nsh"
!include FileFunc.nsh
!insertmacro GetDrives
var newCheckBox
!define NOME "S-Monitor"
Name "${NOME}"
OutFile "${NOME}.exe"
InstallDir "C:\${NOME}"
ShowInstDetails show
AllowRootDirInstall true
;--- Paginas ---
!define MUI_ICON Labels\SetupICO.ico
!define MUI_HEADERIMAGE
!define MUI_HEADERIMAGE_RIGHT
!define MUI_HEADERIMAGE_BITMAP Labels\Header.bmp
!define MUI_WELCOMEFINISHPAGE_BITMAP Labels\Left.bmp
!insertmacro MUI_PAGE_WELCOME
!insertmacro MUI_PAGE_DIRECTORY
!insertmacro MUI_PAGE_INSTFILES
Page Custom CustomCreate CustomLeave
!define MUI_FINISHPAGE_NOAUTOCLOSE
!define MUI_FINISHPAGE_RUN
!define MUI_FINISHPAGE_RUN_CHECKED
!define MUI_FINISHPAGE_RUN_TEXT "Criar atalho na Área de Trabalho"
!define MUI_FINISHPAGE_RUN_FUNCTION "AtalhoDesktop"
!define MUI_PAGE_CUSTOMFUNCTION_SHOW showNewCheckbox
!define MUI_PAGE_CUSTOMFUNCTION_LEAVE launchNewLink
!insertmacro MUI_PAGE_FINISH
;--- Idiomas ---
!insertmacro MUI_LANGUAGE "Portuguese"
!insertmacro MUI_LANGUAGE "English"
!insertmacro MUI_LANGUAGE "Spanish"
Function .onInit
!insertmacro MUI_LANGDLL_DISPLAY
InitPluginsDir
GetTempFileName $0
Rename $0 '$PLUGINSDIR\custom.ini'
FunctionEnd
;--------------------------------
;Arquivos a serem instalados
Section "Instalacao"
SetShellVarContext all
SetOutPath "$INSTDIR"
File /r Ficheiros\*.* ; LOCALIZACAO DA APLICACAO DO S-MONITOR
MessageBox MB_OK "O software BDE (Borland Database Engine) será instalado agora"
ExecWait "$INSTDIR\bde_install_Win7_32_e_64.exe"
FileOpen $1 '$INSTDIR\S-monitor.cpy' w
FileWrite $1 "CPY Location=C:\S-Monitor.cpy"
FileClose $1
writeUninstaller $INSTDIR\uninstall.exe
SectionEnd
Section "Uninstall"
MessageBox MB_YESNO "Deseja desinstalar o S-Monitor?" IDYES true IDNO false
true:
SetShellVarContext all
delete $INSTDIR\uninstall.exe
RMDir /R /REBOOTOK $INSTDIR
Goto +2
false:
MessageBox MB_OK "Desinstalação cancelada."
SectionEnd
Function AtalhoDesktop
createShortCut "$DESKTOP\S-Monitor.lnk" "C:\SMonitor.exe"
FunctionEnd
Function showNewCheckbox
${NSD_CreateCheckbox} 120u 110u 100% 10u "&Iniciar o S-Monitor ao terminar a instalação"
Pop $newCheckBox
FunctionEnd
Function launchNewLink
${NSD_GetState} $newCheckBox $0
${If} $0 <> 0
Exec "C:\S-Monitor\Smonitor.exe"
${EndIf}
FunctionEnd
Function CustomCreate
WriteIniStr '$PLUGINSDIR\custom.ini' 'Settings' 'NumFields' '6'
WriteIniStr '$PLUGINSDIR\custom.ini' 'Field 1' 'Type' 'Label'
WriteIniStr '$PLUGINSDIR\custom.ini' 'Field 1' 'Left' '5'
WriteIniStr '$PLUGINSDIR\custom.ini' 'Field 1' 'Top' '5'
WriteIniStr '$PLUGINSDIR\custom.ini' 'Field 1' 'Right' '-6'
WriteIniStr '$PLUGINSDIR\custom.ini' 'Field 1' 'Bottom' '60'
WriteIniStr '$PLUGINSDIR\custom.ini' 'Field 1' 'Text' \
'Escolha a que disco rígido quer associar a sua licença do S-Monitor.\nA instalação do S-Monitor ficará associada de forma permanente ao disco escolhido.\n\nSe desejar transferir a sua licença para outro PC mais tarde, deverá escolher um disco amovível neste passo.\nSe não sabe que opção escolher, deixe seleccionada a opção por defeito.'
StrCpy $R2 0
StrCpy $R0 ''
${GetDrives} "HDD+FDD" GetDrivesCallBack
WriteIniStr '$PLUGINSDIR\custom.ini' 'Field 2' 'Type' 'DropList'
WriteIniStr '$PLUGINSDIR\custom.ini' 'Field 2' 'Left' '30'
WriteIniStr '$PLUGINSDIR\custom.ini' 'Field 2' 'Top' '64'
WriteIniStr '$PLUGINSDIR\custom.ini' 'Field 2' 'Right' '-31'
WriteIniStr '$PLUGINSDIR\custom.ini' 'Field 2' 'Bottom' '200'
WriteIniStr '$PLUGINSDIR\custom.ini' 'Field 2' 'Flags' 'Notify'
WriteIniStr '$PLUGINSDIR\custom.ini' 'Field 2' 'State' '$R1'
WriteIniStr '$PLUGINSDIR\custom.ini' 'Field 2' 'ListItems' '$R0'
push $0
InstallOptions::Dialog '$PLUGINSDIR\custom.ini'
pop $0
pop $0
FunctionEnd
Function CustomLeave
ReadIniStr $0 '$PLUGINSDIR\custom.ini' 'Settings' 'State'
StrCmp $0 '2' 0 next
ReadIniStr $0 '$PLUGINSDIR\custom.ini' 'Field 2' 'State'
strcpy $R0 $0
StrCpy $0 $0 3
FileOpen $1 '$INSTDIR\S-monitor.cpy' w
FileWrite $1 "CPY Location=$R0S-Monitor.cpy"
FileClose $1
Abort
next:
ReadIniStr $0 '$PLUGINSDIR\custom.ini' 'Field 2' 'State'
StrCpy '$INSTDIR' '$0'
FunctionEnd
Function GetDrivesCallBack
StrCmp $R2 '0' 0 next
StrCpy $R3 '$R4'
StrCpy $R1 '$9'
IntOp $R2 $R2 + 1
next:
StrCpy $R0 '$R0$9|'
Push $0
FunctionEnd