Fatal Error- Call to Undefined Function

It looks like you copied some code from 2010 theme? In 2010’s loop, it references

twentyten_posted_in, which is a function defined in 2010 functions.php

If you copied over the call to that function, but not the actual function, it will blow up like that

Don’t know what you mean by upgrade to 2011.

Have you made this single.php file in your coburns theme?

You basically either need to delete the call to twentyten_posted_in from your single.php

Or you need to copy the twentyten_posted_in function into your theme’s functions.php

Either action would get rid of that error

if you are calling to twentyeleven_posted_in, then you must include that function! lol

If you have a call, you must have a corresponsing function within your own theme… just because the function exists in 2010, or 2011, and those themes are uploaded to your site, you can’t call functions from them. The function must exist in your active theme (or possibly the parent theme if you are using a child theme)

if ( ! function_exists( 'twentyeleven_posted_on' ) ) :
function twentyeleven_posted_on() {
	printf( __( '<span class="sep">Posted on </span><a href="%1$s" title="%2$s" rel="bookmark"><time class="entry-date" datetime="%3$s" pubdate>%4$s</time></a><span class="by-author"> <span class="sep"> by </span> <span class="author vcard"><a class="url fn n" href="%5$s" title="%6$s" rel="author">%7$s</a></span></span>', 'twentyeleven' ),
		esc_url( get_permalink() ),
		esc_attr( get_the_time() ),
		esc_attr( get_the_date( 'c' ) ),
		esc_html( get_the_date() ),
		esc_url( get_author_posts_url( get_the_author_meta( 'ID' ) ) ),
		esc_attr( sprintf( __( 'View all posts by %s', 'twentyeleven' ), get_the_author() ) ),
		get_the_author()
	);
}
endif;

This is the function in question….