If you click on the link in a DataShare Engagement invitation email and get the "Invitation Invalid" message it means this invitation has already been used and the sign up process has been completed for this invitation.
Try signing in to the DataShare portal, you probably already have an account. If you have forgotten your password use the "forgotten password" article to reset your password.
Invitations to join a DataShare Engagement are unique and can only be used to sign up to a specific DataShare Engagement once. You cannot forward an invitation to another user.
If you are new to DataShare and need to be invited to a DataShare Engagement contact your Client Manager.