Error 212 : Name Server Available

[GMG]

Hi all,

I'm trying to update my DNS records at Namesecure and whenever I try
to add my name server I get Error 212 : name server available.

When I try to register the name server for another domain on
register.com I get

Error: You have not specified the name of a valid Domain Name Server.
Please enter a valid Domain Name Server in the field(s) below and
click "Submit" to continue.

The two current and active name servers I run have the name address
for the server and I can do lookups against it but the bollox won't
let me add it to my registrar listing.

I can add other name servers to the list and also delete them.
Something is not right with the server.

What are the registrar's checking for and where could the problem lie?

Any ideas what this means and what can be done about it?

Thanks,

Gavin