Blog Entries missing

Hi,

Bit of a funky problem that I can't quite figure out :

I noticed today that some of our users blog posts were empty - well actually there was no blog post the page loads ok but anything associated with the post itself is blank. It seems to be a random problem affecting users with self made posts and the "Hello World" posts... and yet for some it's fine.

Here's an example of an effected page : http://sceno.org/stu-art/2009/04/hello-world/

Notes :

I discovered that if I created a new page the issue goes away for that user

Admin Activity:

Updated to 2.7.1 yesterday (after testing on test installs) and everything seemed fine then

Installed "Site Shutdown" plugin yesterday while upgrading

Uploaded new theme today (approx 20mins before this issue), essentially whilst being new it was based off one of our existing themes but with the addition of the custom header function. The theme was tested on two of our test installs prior uploading to the live site and has not affected them in any way.

With the issue so randomly affecting blogs/themes I just can't quite figure out what the problem may be, error logs shows nothing to be amiss.