SEF Advance 2008 - Custom 404 Page?

Currently Google has my site indexed with some weird links and when people click on them they are getting this ugly 404 page and I would like to redirect that 404 to a more informational 404 page.

broken google link
www.hosangit.com/how-to/37-windows-relat...indows-xp-sp2-image/

actual link (which makes more sense)
www.hosangit.com/how-to/windows-related/...indows-xp-sp2-image/

I would like to redirect 404 to custom page like (for example)
www.hosangit.com/site/general/error:404/

I enter the link above under
.SEF Advance - Configuration - Replace - Custom 404 page

Now I get the following error
Notice: Trying to get property of non-object in /home/BLAH/public_html/SITENAME/components/com_sef/sef_incl.php on line 0

Any ideas?

Hi, are you sure the page exists on server?
Try to enter a relative link like: site/general/error:404/
Make sure that page physically exists because it doesn't look like something you created.

Also it's better idea to create an uncategorised article with 404 content and select it as default 404 page.

Also, it's possible to automatically map built-in SEF links like this to new SEF URLs if you turn on the option "Redirect built-in SEF URLs" in SEF Advance configurations.