I don't have the tool installed, but last I checked, 5.1 was the newest version of the LDC Client, so that's probably not the issue. As far as contacting the support desk goes, there are several ways for you to do that: you can send the company an email using this address: info@onsoft.de , you can try to reach the live support using this URL: http://www.onsoft.de/en/livesupport.php or you can use the phone by dialing this number: +49 (30) 390 408-0.
In case you're from Turkey, the simplest way to contact Onsoft would be to either use this email address: iletisim@onsoft.de or this phone number: +90 (212) 220 15 12.