Warning: Illegal offset type in isset or empty in (path) line 1097

I was receiving this PHP error at the top of the page whenever I attempted to load any custom post type archives created by CustomPress (Ex: http://www.sampledomain.com/exampleposttype where "exampleposttype" would be the custom post type).

After digging around, I found that this seems to be a problem with the following block of code in core.php lines 181-188

//Archive Page
                if (isset($options['display_post_types']['archive']['post_type']) && is_array( $options['display_post_types']['archive']['post_type'] ) ) {
                        $post_types = $options['display_post_types']['archive']['post_type'];
                        if ( is_archive() && !in_array( 'default', $post_types ) ){
                                if(count($post_types) == 1) $post_types = $post_types[0];
                                $wp_query->query_vars['post_type'] = $post_types;

I believe the problem is related to 'is_archive' so I commented out that entire block of code. It works now, but of course, I will have to keep commenting it out whenever the plugin author updates this plugin, and as of this moment, I have not had an opportunity to see if commenting this out has broken anything else.

Plugin author: see for information that led me to this kludge:

You may wish to implement a permanent fix, as this error is not acceptable for live sites. Thank you.