WPF- What does exit code -1 represents

I have been building a sample WPF Application. I have used some undocumented codes like SetWindowCompositionAttribute() method. Once I run my application it works fine without any problem but when i exit my application using alt+F4 I got a message in the output window.

The program '[10172] Sample.exe' has exited with code -1 (0xffffffff).

I think there is some kind of error occurred. I know that the exit code 0 represents the program executed without any errors.
Does this -1 represents any kind of memory leak? How can i debug and check what error is it causing.

For reference, Here is my code which causes the issue:

public static void SetHBrush(IntPtr hwnd, uint brush) {
    var accent = new AccentPolicy {
        AccentState = AccentState.ACCENT_ENABLE_GRADIENT,
        GradientColor = brush // 0xFFFFFF
    };
    var accentStructSize = Marshal.SizeOf(accent);
    var accentPtr = Marshal.AllocHGlobal(accentStructSize);
    Marshal.StructureToPtr(accent, accentPtr, false);
    var data = new WindowCompositionAttributeData {
        Attribute = WindowCompositionAttribute.WCA_ACCENT_POLICY,
        SizeOfData = accentStructSize,
        Data = accentPtr
    };
    NativeMethods.SetWindowCompositionAttribute(hwnd, ref data);
    Marshal.FreeHGlobal(accentPtr);
}

Here is the link where i have fetched the code : sample-win32-acrylicblur