question re: “categories”

I changed my email programme to "Windows Live Mail". In my former programme I had "groups" where I was able to send messages to multiple addresses at the same time. I have put those groups into my new programme but was not able to send messages to the groups - the programme told me I must enter addresses instead of the group name. Then I figured out how to do it and it worked, sending from the "contacts" page. Now it has stopped working and I am unable to send to my "groups" again, known as "categories" in this new programme. Can anyone advise me? Thanks