Attachments to Outlook emails

I get two different kinds of error messages with attachments. The first of
these says, when I click on the attachment to open it, that it can't find the
attachment. Then after I get back to the email showing the attachment, and
then click on the attachment a secont time, it opens. Why?

The second error message comes after I have finally opened an attachment.
When I try to close the attachment and the email from which it came, the
message says something to the effect of "File has been changed. Do you want
to save the changes?" I always answer no in order to go on, but I am
concerned about what kind of changes this is talking about. Ideas?