Why can't group members enter the sim, that is owned by that group?

[GreySchoolofWizardry]

I recently switched ownership of our private sim from this avatar, to group owned. I had to create a new group. The old group allowed everyone onto the sim, but it was owned by someone who was no longer part of our group. We could not have the original group own the sim. 

The land was transferred over to be owned by our new group. The settings under access are for our new group. Everything seems to be set up right. 

However, a handful of avatars that are in the group cannot enter the sim. Some of us can. All have the group activated. One avatar was able to be on the sim for hours last night, then suddenly, she could no longer be on sim. 

Any idea what's happening?

[Alwin Alcott]

check if accidently, public access ánd groupacess is selected, at sim and parcel level.