You expected focused and detailed replies based on the dearth of
details in your post?  You provide no details, like:

- WHICH version of Outlook.
- WHICH version of Windows.
- What e-mail client and OS the recipient is using.
- WHAT type of object is being attached.
- HOW the object is being attached to the e-mail (copy-n-paste, Insert
menu, drag-n-drop, etc.).
- WHAT plug-ins are installed and active in Outlook.

Read:
http://66.39.69.143/goodpost.htm
http://support.microsoft.com/kb/555375
http://users.tpg.com.au/bzyhjr/liszt.html

We aren't there looking over your shoulder to see at what you are
pointing your finger.