IEuser.exe - Bad Image

When opening .PDF files from a website, we receive the following error on a

Windows Vista Ultimate computer:

IEuser.exe - Bad Image

c:\Program Files\Windows Defender\MpOav.dll is either not designated to run

on Windows or it contains an error. Try installing the program again using

the origional installation media or contact your system administrator or the

software vendor for support.

User is logged in as administrator

Windows Defender is disabled

This error occures every time we try to open a .PDF file from a website.

Any suggestions? Many thanks!