Hello Nancy,
Did you get the above message after the posts got deleted or during deletion?
If it is happening after the deletion, then it may not be associated with the Bulk Delete plugin.
Are you able to view the ‘All Posts’ page now or is it consistently giving the error for you?
You can check the PHP error log in your server to see what is the reason why PHP is giving that error. Once you post the error here I can give you instructions to fix it, even if it is not caused by our plugin.