After migration from D5 to D6, TAC is denying access to nearly all pages for anonymous users.

This is actually driving me crazy because we tested the migration on a backup of the website first, and that site does not have the problem.

Basically, when you're logged in things work fine, but if you're not logged in something like 99% of the site is access-denied, with no clear explanation of why.

1. I've rebuilt permissions several times.
2. Uninstalling TAC restores anonymous access but, obviously, also gives anonymous users access to areas of the site we don't want to give them access to.
3. Reinstalling TAC reintroduces the problem.
4. Looking at the issues for TAC I noticed similar complaints related to the PHP version. Both the test site (which works) and the production site (which is broken) are using PHP 5.2.17.

Question: When I re-installed TAC, it restored the old schemes. Is it possible to completely remove these schemes? Would it help?

Question: When I reinstalled TAC it "remembered" the previous schemes it had installed. Is it possible to uninstall the schemes completely? Would it help?