Dns problems..

I have a domain registered at Moniker.com which is pointing to my Siteground server.

At Moniker, I entered the Siteground nameservers... and I keep getting "Missing Nameserver errors" when I check at http://www.intodns.com/teachmymind.com if the domain is pointing properly to Siteground.

Check if the dns is pointing properly, is should look like one of my other domains which are pointing correctly:
http://www.intodns.com/freyer.com

Despite several support queries, I still don't know why these errors appear.

The result is that the domain is up for a day or so and then down for a day, then up again...

Would appreciate any help or suggestions.

thanks,
Riggie