admin Products category filter dropdown causes blank screen

Hi
Hope you can help.

Since the last couple of updates when we use the category filter dropdown in products, when in admin, we get a blank screen. Checked the error log and we are getting

PHP Catchable fatal error: Object of class WP_Error could not be converted to string in /.../public_html/wp-includes/pluggable.php on line 894, referer: http://www.peggyjane.co.uk/wp-admin/edit.php?post_type=product

As there are quite a few products this is causing my client some annoyance and a fair few emails to me.

I'm getting the same problem in a new install I starting to set up for a new client.

I know there have been some changes to the filter category recently.

Grateful if you have any suggestions.

Thanks

Leonie