app.focus() resulting in negative x and y values

So I'm using app.focus() to focus on an application for memu, and it results in an error like this:

[error] Region(-250,-250,125,125) outside any screen - subsequent actions might not work as expected
[error] script [ C:\Users\Yongho Lee\Desktop\GFL\GFL.sikuli ] stopped with error in line 156
[error] java.lang.NullPointerException ( java.lang.NullPointerException )
[error] --- Traceback --- error source first
line: module ( function ) statement
123: main ( focus_window ) while not (memu_window.exists(Pattern('main_menu_home.png').exact())):
145: main ( collect_exped ) focus_window()
[error] --- Traceback --- end --------------

The problematic portion of the code looks like this:

def focus_window():
 global memu_window
 myApp = App.focus("MEmu")
 memu_window = myApp.focusedWindow()
 memu_window.setAutoWaitTimeout(1)
 loop_count = 0
 while not (memu_window.exists(Pattern('main_menu_home.png').exact())):
  myApp = App.focus("MEmu")
  memu_window = myApp.focusedWindow()

It's supposed to focus on the memu window and return back its coordinates to another function.

The error occurs when the code tries to initiate (memu_window.exists(Pattern('main_menu_home.png').exact())), so I'm assuming the problem here is app.focus("MEmu") returning negative values. Why does this happen and how can I fix it?