You can probably do in this ugly way:
code:
var result = Interop.Call("User32.dll", "MessageBoxW", 0, "Your account has been disabled. Do you want more infomation?", "Error!", 16+4);
// Get window handle to MessageBox
var hMessageBox = Interop.Call("User32.dll", "GetForegroundWindow");
// Apply TopMost
Interop.Call("User32.dll", "SetWindowPos", Handle, -1, 0, 0, 0, 0,19);