I am experiencing this as well. It appears to be a similar problem I had with FriendStream for my HTC. For some reason, HTC Sense does not seem to sync up a few of my contacts properly. When on FriendStream, I cannot see their wall posts. FriendCaster seems to feed off FriendStream and anything missing in FriendStream is missing in FriendCaster as well.
I do notice that I get alerts through FriendCaster as I set it up to notify via Gmail. When I get the notification and try to open up the post, I get an error indicating that there is an issue with permissions. If I go to my HTC contacts, I find that I cannot access those contacts' info page. I get barely any information. For those contacts whose posts I can see, I get way more information.
When I had this issue with FriendStream before, I find that after a week, these contacts mysteriously work again and I can see their wall post on FriendStream. I'm not sure exactly what I did to make it work again.
What I'm going to do is continue to use both for now. FriendCaster has enough features that I want to keep it around. It also handles my notifications well and deletes my notification emails so as not to clutter up my Gmail inbox. I'll probably use the Facebook for viewing posts and FriendCaster to check likes and other features that the Facebook app does not have.
By the way, I am using an HTC Desire Z, standard non-rooted.