Please follow the steps below:

1. Open the class.WMUHelper.php file in /wp-content/plugins/wpdiscuz-media-uploader/includes/ folder

2. go to line 460 

3. Find the imageFixOrientation function and replace with the following one: 

public function imageFixOrientation($filename) {
        if (function_exists('exif_read_data')) {
            $exif = exif_read_data($filename);
            if (!empty($exif)) {
                $image = imagecreatefromjpeg($filename);
                switch ($exif) {
                    case 3:
                        $image = imagerotate($image, 180, 0);
                        break;
                    case 6:
                        $image = imagerotate($image, -90, 0);
                        break;
                    case 8:
                        $image = imagerotate($image, 90, 0);
                        break;
                }
                imagejpeg($image, $filename, 90);
            }
        }
   }

I'd also recommend you install the exif library, as the wpDiscuz Media Uploader add-on uses exif library so as to allow images to be uploaded in the right way. For example, if you take a photo with IOS it rotates when you publish the comments.

please send the login details to infogvectors.com email address. 

Your Email adress for Admin-account?

Could you please provide us the admin login details for deeper support? 

I've already asked the add-on developers about the issue. They are going to check it. Please wait for a while I'll update the topic asap. 

Have transformed a jpg to png (see my last post) and it worked

I used Chrome Browser

We've tried several times and it seems, it's working fine. Could you please tell me a little more about the issue? And when exactly are you running into this error?

Testing comment: https://www.riverboating.com/gaestebuch/#comment-111