NSIS window disappear - nsis

Question

I have tried a lot of possibility with this code but it doesn't work. I need to check a VPN connection. If I run the code firs time it works, but if I don't restart the program and push the button secondly then the program just disappear. Any idea how to fix it? thanks.
Function VpnLoginWindow
${Do}
!insertmacro VpnLoginWindow
StrCpy $4 0
${If} $3 == 1
${Do}
!insertmacro VpnLoginWindow
StrCpy $4 1
StrCmp $3 "0" 0 +2
${ExitDo}
${Loop}
${EndIf}
${If} $4 == 1
${ExitDo}
${EndIf}
${Loop}
FunctionEnd
!macro VpnLoginWindow
StrCpy $5 $1
System::Get "(i.r1) iss"
Pop $R0
System::Call "user32::EnumWindows(k R0, i) i.s"
${Do}
Pop $0
StrCmp $0 "1" 0 +2
${ExitDo}
System::Call "user32::GetWindowText(ir1,t.r2,i ${NSIS_MAX_STRLEN})"
StrCpy $2 $2 7
StrCpy $3 0
${If} $2 == "SSL VPN"
StrCpy $3 1
${ExitDo}
${EndIf}
Push 1 # callback's return value
System::Call "$R0"
${Loop}
System::Free $R0
StrCpy $1 $5
!macroend

Answer 1

Callbacks are tricky to get right and the plug-in is a little buggy. Also, you should not use relative jumps to jump over macros like ${ExitDo}!
!include LogicLib.nsh
!macro FindVpnLoginWindow
Push "" ; Result: Window not found
System::Store S
System::Get '(p.r1, p)ir0r0'
Pop $9
System::Call 'USER32::EnumWindows(k r9, p 0)'
${Do}
${IfThen} $0 != "callback1" ${|} ${ExitDo} ${|} ; <-- adjust the callback# if required
StrCpy $0 1 ; Set callback return value, continue search
System::Call "USER32::GetWindowText(pr1, t.r2, i ${NSIS_MAX_STRLEN})"
StrCpy $2 $2 7
${If} $2 == "SSL VPN"
Pop $2 ; Throw away old result
Push $1 ; Result: HWND
StrCpy $0 0 ; Set callback return value, stop enum with 0
${EndIf}
System::Call $9 ; Return from callback function
${Loop}
System::Free $9
System::Store L
!macroend
Function BackgroundFindWindow
!insertmacro FindVpnLoginWindow
Pop $0
DetailPrint "Result:$0"
FunctionEnd
...
GetFunctionAddress $0 BackgroundFindWindow
BgWorker::CallAndWait
GetFunctionAddress $0 BackgroundFindWindow
BgWorker::CallAndWait