For groups where you need to be a member to access some or all of the features, Yahoo! requires members to use a Yahoo! ID to access the Web features of the group. If you do not yet have a Yahoo! ID, you will need to get one. If you have multiple Yahoo! IDs, you need to be logged into Yahoo! with the ID that you used when you joined your group. Check the "Welcome" link that appears at the top of all Groups pages to ensure that you are logged in with the correct ID.
Alternatively, you may need to associate your Yahoo! ID with the email address you use for the group to get web access. To do so, follow the instructions to "get web access" on the page that indicated you were not a member of the group and then follow the appropriate instructions.
If you are not yet a member of the group, you will need to become a member before gaining access to any of the member only features.