When you attempt to open an attachment in Outlook, you receive:
The file file name does not have a program associated with it for this action. To create an association, double-click My Computer on your desktop. On the View menu, click Options, and then click File Types.
This behavior can occur if the attachment has no extension, like MyAttachment, instead of MyAttachment.txt. This behavior can also occur if the attachments extension does not have a registered program on your computer.
To workaround this behavior, right-click the attachment and Open With an appropriate program, or install the appropriate program.
NOTE: To associate NOTEPAD.EXE with a nul extension, use REG.EXE, built into Windows XP and Windows Server 2003, or REG.EXE from the Windows 2000 Support Tools on the CD-ROM, and type:
reg add "HKCR\." /VE /T REG_SZ /F /D JSIINC reg add "HKCR\.\JSIINC\shell\open\command" /VE /T REG_EXPAND_SZ /F /D "%SystemRoot%\system32\NOTEPAD.EXE \"%1\""