I have some sites that have been idle with either 404's or 403's. With the last update Google changed the Page Rank to zero. I have populated the sites with pages in hopes that Google will recognize the existing backlinks and return the previous Page Rank. Has anyone else been through this cycle or is this something new?
I've seen this happen - I'd add more content to the 404's making a site map or a set of links to several key portions of your site.
You're getting a PR because a 404 or 403 tells Google that it shouldn't index those pages. If you populate those pages than you should be fine. BTW why do you have links to 404 or 403 pages?