Thanks Krileon(Kyle) for your response.
I have successfully upgrade to Joomla 1.5.20 and CB_1_2_3, but the problem still exists.
As per my orignal posting, the Login produces the 404 screen I providedin the attachment (in IE 8 only, but does complete the Login otherwise - it's as if it is a final step error. It shows "Error on Page" at bottom left of screen. My site is
www.aus4017.com. Probably needs Firebug analysis, which unfortunately I am not yet competent at.
Most annoying to IE users, which is obviously the majority out there.
I'm happy to provide Login details via private email if that will help. Need to fix it quickly as I am in prelaunch.
Thanks in advance for any help.
John