Can't access wp-admin/network after installing Domain Mapping plugin

Hi

I've installed the Domain Mapping plugin and mapped my original blog addresses to new domains. Now I don't seem to be able to access the network admin - I just get redirected from myOldDomain.com/wp-admin/network to myOldDomain.com/wp-login.php and from there to myOldDomain.com.

Also, which I guess is related, I can't hit the dashboards of any of the blogs except the main one.

Where am I going wrong?

Many thanks.