standard toolbar changes when I send a do***ent as an attachment

I'm using Outlook 2003. 
I set up a toolbar button to activate a macro on the standard toolbar. 
This 
works fine.  However,  I noticed that when I'm in a Word do***ent or Excel
or 
other program and choose to send that particular do***ent as an
attachment, 
my macro button disappears from the standard toolbar.  If I try to get it 
back, I don't see the macro under the tools/macro menu.  Why would that be

and how do get it back?

Thanks!