I can only post on walls on my iPad. I dunno why but I can't post on them on my PC atau laptop. Its weird. Its probably a glitch with the site but its been like this for awhile. I have read that other users have been reporting similar problems to the Fanpop team but still no change.
Actually, I messaged Micheal (one of the creators of Fanpop) and he's fixing it right now. It could be the browser you're using atau the "internet security" like Norton anda may have. It might take awhile but I keep anda updated.