sudden message 'please use valid z co-ordinate'

Hope this is the right forum - cannot get an answer from LL to my ticket. I run a large school and recently changed one boundary on a patch that is used as a landing point for classrooms. Now, although the landing point didnt change at all, I suddenly get a 'please use valid z co-ordinate' message and can no longer post notices in events about upcoming classes. No-one will help me, I am totally at a loss.

Perhaps try changing the landing point, if only slightly, to see if it resolves.

The z co-ordinate is the height. Did you change the level of the land; if so is the existing landing point now underground?

And what Kenbro says.