Outlook 2010 Converts .jpg to .windat

I've a 64 bit Windows 7 machine using Outlook 2010 for my business (via Microsoft Exchange Server) and personal (via POP3). Some recepients get my .jpg and/or .docx attachments as windat files. I've tried HTML, Rich Text & Plain Text to no avail. I done the following solution and had some success sending files:

Located and selected the following registry subkeys:
HKEY_CURRENT_USER\Software\Microsoft\Office\12.0\Outlook\Preferences
On the Edit menu, point to New, and then click DWORD Value.
Type DisableTNEF, and then press ENTER.
Right-click DisableTNEF, and then click Modify.
In the Value data box, type 1, and then click OK.
Exit Registry Editor.
Restart the computer.

Anyone have any ideas what I'm not doing properly?

Many thanks,

Mike

Thank, Guy. I'll give that a shot.

Mike