You receive the “Interface not registered” error message when you try to send or to save an e-mail message to the Drafts folder in Outlook 2002.

Solution:

To resolve this problem, register the Ole32.dll file. To do this, follow these steps:

1. Click Start, click Run, type the following command in the Open box, and then click OK:
   Regsvr32.exe %Windir%\System32\Ole32.dll
2. In the RegSvr32 dialog box, click OK.

Source: http://support.microsoft.com/kb/870707