DNS Problem? Error 1502

I have a PING-probe from NL to my Webserver at www.christingercars.ch and the scanner tell me that it cannot resolve the FCDN. Any other nslookup-Server in the internet can resolve my hostname? Which DNS-Server do you use to resolve the hostnames? The name resolution/scan worked until the 18th February 2015. Since then I get the following error message:

Name lookup failed
Error code: 1502
Failed to resolve the domain name. This may mean that the domain name is mistyped in the Monitor settings, the domain is not reachable from the Internet or the corresponding DNS entry is not valid or expired.

Best Regards
Fredy