group member problems

hi.
i've added some groups to my forum, but i am having a problem with adding members. when i added a member to one particular group, after a while, or when they log on, for some weird reason they are removed from the group back to a normal person.
so i have to keep adding them back on?
why is it doing this?

please help!!!

are they closed or open groups? i think that mite make a difference, maybe the group mod is removing them or they are removing themselves

it is an open group and i am the mod. but i've just received an email to request permission for the member to join the group. i didn't get any of those before, so it might work now...

nope! it hasn't worked!