When you send an attachment by right clicking on it and choosing Send, newer versions of Windows add a block of text to the message body. The text is added by the sendmail.dll and varies with your version of Windows, the same file that is used by Internet Explorer to add an attachment as a shortcut instead of a text link.
Unfortunately, you can't remove this message text. To quickly erase the text use Control+A to Select All and begin typing.
For workarounds (which eliminates other issues as well), see Tip 854: Another SendTo shortcut method, Tip 361: Sending Files From Windows Explorer, and Create a Custom Send to Shortcut.
Published October 7, 2003. Last updated on December 27, 2013.