PHP Catchable fatal error

[gemini]

A few days ago I explored the Role Scoper Plugin a bit (I had some conversation with Daisy). I encountered the error below and the RS developer provided an update, which I thought fixed the issue. I got in more issues with this plugin and I removed it for now (including tables in db).

PHP Catchable fatal error: Object of class WP_Error could not be converted to string in ... /public_html/blog/wp-content/themes/streamline_30/tools/breadcrumbs.php on line 59

code line 59:
$output .= '<a href="'.get_category_link($cat->term_id).'">'.$cat->name.'</a> '.$sep.' ';

Now the error happens again sporadically. I thought, when I am writing a new post, but I couldn't proof this either. I tried disabling all plugins as well, couldn't find the source.

I thought posting to Twitter from WP could leave the port open, when Twitter is busy and produce an error. On one site I removed Twitter Tools and this site shows still similar behavior to the error.

I there any place I could look into?

http://www.ip-192.com/