[Plugin:Wp-dtree] Cannot modify headers error

I’ve just moved my wordpress site to a new provider. Most everything is working properly, however, when I try and save or update a post/page I get this error:

WordPress database error: [Query was empty]

Warning: Cannot modify header information – headers already sent by (output started at /home/xxxxxx/public_html/wp-includes/wp-db.php:517) in /home/xxxxx/public_html/wp-includes/pluggable.php on line 850

If I disable wp-dtree everything works fine (the post actually does save even with the error, but it ain’t pretty).

Wp-dtree itself actually works just fine as well (I’ve also verified the wp_dtree_cache table is present and that the related rows exist in wp_options).

Any ideas how to fix the errors?

Thanks,
Tony