Groups of email names in Windows Live Mail

I have a group of 79 emails that was created in Outlook Express some time ago.  The list was successfully transferred to Windows Live Mail and I have added ma,es to  it.  However, whenever I create an email specifying that it go to that list, the program only sends it to a few of the people on the list -- the rest are dropped.  I've tried breaking the group into several smaller groups and specifying that the message be sent to all the people in all of the groups, but the program takes a few names from each group but not all.  How do I fix this?