standard toolbar changes when I send a document as an atta..

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 document or Excel or
other program and choose to send that particular document 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!