Display our own error pages in Portal

Hi,

How can I modify the standard error pages that are displayed when an error occurs in portal?

Or

How can I display my own error pages instead of sap standard error pages?

Where the sap standard error pages are stored in portal?

I have already gone through the link

http://help.sap.com/saphelp_nw70/helpdata/EN/47/1d5a4390524403e10000000a1553f6/frameset.htm

for Modifying Error Pages but I couldn’t locate the path System Administration ->System Configuration - >Knowledge Management -> Content Management ->Web Page Composer ->Error Pages ->Error Pages.

I want to perform same task as described in this link.

Kindly help.

Regards,

Madhvika Joshi