Multisite & domain mapping - logs user out between network sites

Hi

Have now set up a multi-site network and as a final stage, just activated and configured the Domain Mapping plugin

This went well and mapping is working fine, but ....

a. pre-installation - a user logged in on Site A would stay logged in when navigating to any of the other sites in the network - B, C, D etc.

b. post installation - the user is now being logged out when leaving any of the network sites to navigate to another.

Really want to the user to stay logged in across network but cannot figure where / what settings I need to adjust.

Appreciate a pointer on this one please.

Thanks.