There should be no reason for the page to redirct to the insufficient permisions page for these pages as the test for being allowd is carried out in the common.asp include file that is used throughout the section, the only way you can losse access to some pages is if cookies are not being crrectly set and read.
IE does have many issues with cookies, try deleting all temporary internet files, then delete your cookie cache, this should reset IE's cookie index and hopefully prevent the problem.
Also try another web browser and see if the problem persists.