Command not working on Win XP

From: Steven (anonymous_at_discussions.microsoft.com)
Date: 11/29/04 

Date: Mon, 29 Nov 2004 17:47:42 +0530

My application is in VBA, and uses the AppActivate command. It works fine on
all environments and OS, except Win XP. This particular command fails on XP.
I have heard XP is more secure... is there any security related issue or any
setting I am missing ??
I dont have any SP on the Win XP machine.
Please suggest.