Problems with customers not staying logged in

Hello there,
I dont know what I did wrong or what happened after I upgraded from 1.39h to 1.5
I follow the instructions without any problems 1100 diferent items on the database and around 200 customers and around 200 orders or more.
ALL has been imported with any problems some worning on database upgrade as aticipated on the tutorial. Uploaded a test template working fine all works fine EXCEPT for:
Customers log in and accept log in credentials BUT if they click on my account comes back to LOG IN page.
same as when I add a product to shopping cart, I want to check out and takes me to log in page . I enter user/customer credentials, I log in without problems, hit CHECKOUT and again to LOG IN Page :cry::cry:

Many add ons on original 139h version but are working, is it possible that ruins the upgrade any lifesaver please