Theme error - Recoverable fatal error: Object of class stdClass could not be converted to string

Anyone know what could be causing this error?

My custom theme works fine until used as an anonymous user in maintenance mode. Custom theme is the problem though.

I just don't know why it would be causing issues with template_preprocess_maintenance_page ... I'm not even using custom maintenance-page.tpl.php and my settings.php is setting $conf[maintenance_theme] = 'bartik'. If i set bartik as my default theme my maintenance page is displayed, if my custom theme is set, maintenance page is WSD, after switching back to bartik as default theme, this error is displayed:

Recoverable fatal error: Object of class stdClass could not be converted to string in template_preprocess_maintenance_page() (line 2708 of theme.inc).

Line 2708:

isset($variables[$region]) ? $variables[$region] .= $region_content : $variables[$region] = $region_content;