Problem sending an attachment using dbo.sp_send_dbmail
You can check the database mail log by going to management -> right-click database mail -> select view database mail log.  Any errors should be in here, for example:


  Message
  The mail could not be sent to the recipients because of the mail server failure. (Sending Mail using Account 1 (2014-05-16T02:21:47). Exception Message: Cannot send mails to mail server. (A recipient must be specified.).
  )


Also, you could fire up SQL Server Profiler to check the user for sp_send_dbmail.  I think it uses the current user account to send the mail, so I would also confirm your windows account has permissions to the file.