It seems that if you check the "Enable Private Messaging" box, this covers it all, since I have it checked and have never had a problem sending or receiving. However, there is another, different box that will only allow PMs from mods and contacts, so maybe checking that one instead is what causes the problem?
Thanks for the info--it's one of those areas of the forum that I seldom venture into, kind of a "set it and forget it" thing for me! Good reminders to check on everything once in a while to make sure I still want those particular options...