Broken admin order page after installing the extension

If Amasty Order Attachments extension is enabled, please edit /app/code/local/Amasty/Orderattach/Model/Observer.php 

Replace 

        if ($this->_isInstanceOf($block, $this->_orderViewClasses)) {
            $html = $this->_prepareBackendHtml($html);
        }

with 

        if ($this->_isInstanceOf($block, $this->_orderViewClasses) && !($block instanceof Fooman_Connect_Block_Adminhtml_Sales_Order_View_Tab_Xero)) {
            $html = $this->_prepareBackendHtml($html);
        }