Wheelup not working on a specific sub window

[lunalr]

Hi,

I want this command to work on a specific sub window (ClassNN: TPluginForm1):

#IfWinActive ahk_exe FL.exe

Numpad7::
sendWheelUp:= true
while (sendWheelUp) {
send, {WheelUp}
sleep 500
}
Return

Numpad7 up::
sendWheelUp := false
Return

The command works on any sub window except for this one: ClassNN: TPluginForm1