New Multisite not found

Hi, i’ve recently tried to add a third site onto my multisite setup.

Everything seems fine; i receive the relevant emails advising me of its creation but when i try to access the backend or frontend it just says page not found.

i’ve also noticed that the original virtual sub-domain of my second site has disappeared from the mapping plugin and i cannot revert to if i so choose.
it has been replaced by the mapped domain !

any ideas ???