WordPress MU

Fatal error: Call to undefined function post_class() in /home/emperor/public_html/wp-content/themes/default/index.php on line 15

I've looked at line 15 and can't see what's wrong. Any suggestions please?

And what is there on line 15?

I thought I had this fixed, but I don't. If I change themes it goes away so apparently it's only the default that is bad.

This is what is on line 15:

<div <?php post_class() ?> id="post-<?php the_ID(); ?>">

Where along the process does this occur?

Is this for new users trying to sign up? New blogs generated on the backend?

Is this default theme the standard one included with the zipped download or one that you installed? I ask that since I just had the issue elsewhere and the admin had changed the theme and forgot to mention it to anyone. :)

This is for new users signing up. The process works fine all the way up to logging in and getting the dashboard. When they click on "view site" they get the header and the error message just below it.

This is the standard theme that is the default.

Thanks for the help.

Bob

Some poking around with google shows post_class to be a 2.7 function. If this is an upgrade, how did you upgrade? What version of mu are you running?