Catchable fatal error:

[LucySofiano]

Catchable fatal error: Object of class WP_Error could not be converted to string on my site http://www.sofiano.com

Hi I've been doing some searching around ref my 'Homepage' request earlier which relates to the problem I'm experiencing.
For your ref - My posts are assigned to categories. The only plugin installed is Featured Content.
When I go to Theme Options to select Homepage Featured categories the fatal error is dispalyed and I can't restore my original settings.

An answer related to this on a different forum was given as:

The issue has to do with PHP 5.2+ breaking certain backward-compatibility of converting a PHP 'object' to a text string. You either need to downgrade below 5.2, or the code where the error occurs needs to be 'properly fixed' to address the change (the fixes should then work on any version...).

I can't help debug random code, so go to the authors and tell them to test and fix against 5.2 or later

I don't know how to downgrade so if you can verify this as a 'fix' please would you either explain to me how to downgrade my PHP or debug the code and provide me with a solution.
Thanks