MX issue (IP error)

[Mapu]

I have recently added this zone record (names changed to protect the
innocent):

@                       IN      SOA     ns2.isp.com. root.ns2.isp.com. (
                        1999072001; Serial
                        43200 ; Refresh
                        3600 ; Retry
                        604800 ; Expire
                        86400 ) ; Minimum

                        IN      NS      ns2.isp.com.
                        IN      NS      ns2.mci.net.

                        IN      MX      0 srn.ne.mediaone.net.

                        IN      A       srn.ne.mediaone.net.
www                     IN      A       srn.ne.mediaone.net.

Upon restarting named, the following error shows:

Jul 20 10:50:37 as4100a named[712]: reloading nameserver
Jul 20 10:50:38 as4100a named[712]: customers/domain.org.zone:13: IP Address
error (srn.ne.mediaone.net.)
Jul 20 10:50:38 as4100a named[712]: customers/domain.org.zone:14: IP Address
error (srn.ne.mediaone.net.)
Jul 20 10:50:38 as4100a named[712]: master zone "domain.org" (IN) rejected
due to errors (serial 1999072001)

srn.ne.mediaone.net resolves- so I'm not quite sure as to the error. Any
help would be appreciated.

Michael