2.6.2 Admin – can’t access old posts – blank page

Hi,
I created a couple of posts on WordPress 2.6.2 and they worked fine, I could go back to Manage > Posts and edit them.

All of a sudden, when I click to edit certain posts I get a blank page.
The top navigation is there, but that’s it.

This doesn’t happen to all posts, just certain ones. And if I recreate that same exact post again, I can edit it for a couple of hours, and then the page turns blank again.
It happens consistently with the same posts.

Any ideas?

Thanks very much,
Jenny