Hi, m using MS Office 2007std edition. and when i try to attach xlsx files in a new message (also in forwarded/replied messages), it gives a warning pop up like "one of the attached files is opened by another program. if you chose to continue sending any modified data will not be sent" (Or something like that). I tried this: hkey_current_user\software\microsoft\office\12.0\outlook\options\general new string value: ExtensionsToExcludeFromTracking modify and add xlsx there. this did not help. What should be my next step?