Thanks guys for your help, Actually, it seems a bit more complicated than just focus/blur. As a matter of fact, my perl program works fine with just about everything except Outlook SR1 9.0.0.3821. The program does even detect that Outlook is open by using GUI properties (Outlook's class name : rctrl_renwnd32). For instance, the following bit of code works fine :

return Win32::GUI::GetClassName(Win32::GUI::GetForegroundWindow());

So far the only property that doesn't seem to work is

$app = Win32::OLE->GetActiveObject('Outlook.Application');

Besides, Zero Flop, thanks for reminding me about the die or warn - but I don't need it since I analyse the return value for $app - if it's undef then it's not open.