If you check your site at
http://www.dnsreport.com you will find you
have one or more missing (stealth) nameservers. The following
nameserver(shttp://www.dnsreport.com/) are listed (at your nameservers)
as nameservers for your domain, but are not listed at the the parent
nameservers (therefore, they may or may not get used, depending on
whether your DNS servers return them in the authority section for other
requests, per RFC2181 5.4.1). You need to make sure that these stealth
nameservers are working; if they are not responding, you may have
serious problems! The DNS Report will not query these servers, so you
need to be very careful that they are working properly.
ns2.ipowerdns.com.ns2.ipowerweb.net.
My opnion is to change your hosting servers.