Domain Mapping > http:// works fine but www. diverts to random post

Hi Guy's,

This ones git me miffed!

WP Multisite Install > Latest Domain Mapping Version.

On 1 site only directs fine however the directs to a random post (it changes).

Have pinged both urls and they hit the correct ip address.

As I said this ones got me miffed!

Any help / advice as to where to start working this out would be great.

Many thanks