lucy24 - 7:16 am on Jul 9, 2011 (gmt 0)
I click on a random link (it is a valid URL) and it returns a 404. It doesn't matter where the link comes from, put it in the browser address bar and get a 404. Refresh the page again and again over a period of time still a 404.
In another browser tab go to the website main URL and then drill down through the directory structure and find the page in question. It is there and valid, no error.
Both URLs are identical.
If I now go back into the browser tab with the 404 page and refresh I now get the correct page displayed!
Here is another analogy to contemplate.
Have you ever seen a Forums post (not here, but in forums that allow image posting) where there was supposed to be a picture, but instead everyone sees some form of "you can't do that" message from the image host? The person who put up the original post has no idea this is happening; the image comes through loud and clear for them. If you are curious enough to go to the site where the image lives, starting on the front page, and navigate through the links, you eventually get to the picture, clear as day. Now refresh the Forums page and the picture jumps into view.
It refreshes because it is now a matter of record, via a cookie or some other means, that you obtained this image by Authorized Means and are therefore allowed to reload it.
What you're seeing might be the identical behavior. You just need to figure out what's triggering it.