src/Web/ClientProxy.php
public function showErrorMessage($errMsg)
    {
        if (!$errMsg) {
            return;
        }
        if ($this->isRpc) {
            $_GET['ob_err_msg'] = $errMsg;
            ob_end_clean();
            $form = "common.form.ErrorPopupForm";
            $html = Openbizx::getObject($form)->render();
            $html = $this->buildTargetContent("DIALOG", $html);
            $this->_formsOutput[] = $html;
        } else {
            $this->_errorOutput($errMsg);
        }
    }
public function showErrorMessage($errMsg)
    {
        if (!$errMsg) {
            return;
        }
        if ($this->isRpc) {
            $_GET['ob_err_msg'] = $errMsg;
            ob_end_clean();
            $form = "common.form.ErrorPopupForm";
            $html = Openbizx::getObject($form)->render();
            $html = $this->buildTargetContent("DIALOG", $html);
            $this->_formsOutput[] = $html;
        } else {
            $this->_errorOutput($errMsg);
        }
    }
Show error message.

If its a remote call, it uses javascript
If it is not a remote call, it outputs to the page's html

@todo Hard code for error form : "common.form.ErrorPopupForm"
change to flexible ErrorPopupForm, save in Class variable and maybe also in configuration

@param char $errMsg
@return void