Group IMS - I don't receive most of them.

I belong to several schools on SL, and whenever they post a class, the IM rarely reaches me. As far as I can see, other groups I belong to (non educational) have no problem reaching me, but the ones I'd really like to see just don't make it. I also teach at one of the schools, and there is a problem with some of my own group IMs going out when I announce a class.

What can I can do? I've left the groups and joined them, but I'm still not getting the IMs.

This has been going on for several weeks now, incidently.

Thanks.