Groups not adding to contact list

My husband joined a group 2 weeks ago and can't get it to show in the contact list. When he received the invite, he accepted and got an error that said he couldn't join he was already a member. Now if I view his profile, the group is in the list. When he goes to switch to that group so he can set up a vendor stall, he doesn't show it in his contact list.

We've tried logging him from both his pc and mine and get the same results. Also we have cleared cache and uninstalled / reinstalled SL. Any ideas on what we should do next? TIA

Can he contact the group owner and get him/her to remove and re-add him?

Thanks for the reply Oryx. We'll try that suggestion.