The hosting company has confirmed the problem and recommended as a temporary workaround to replace the nameserver at the /etc/resolv.conf with IP 188.8.131.52. This is the public nameserver from google. The problem is fixed then for TSViewer.com for now. As soon the nameserver from the hosting company is queryable again it will be used again here.
I apologize for this unpleasant problem. I noticed it a little late, only about 2 hours after the problem occured.
The original nameserver is now back in service and is being used again by TSViewer.com.