I recall reading somewhere that one of the plugins you have activated, buddystream, is messing up with activity page. Change to bp-default theme and deactivate buddystream and see if same behavior applies. If you have bp-custom.php in your plugins folder, rename it in the meantime.
I have the same problem here. I’ve deleted the buddystream plugin and the problem is still exist. Any help?
I just installed wordpress 3.1 and then I installed buddypress, and the Fishbook theme, nothing else, when I try to post a comment I get the same page not found error, with both the default theme, and the fishbook theme.
I deleted buddypress all togehter and reinstalled with the standard theme and receive the same message.
I have exactly the same problem 
. After replying on some activity post I get Page not found. I have latest Buddypress and wordpress with default theme and have never had Buddystream installed.
@gian-ava
13 years, 1 month ago
I am experiencing a weird problem on http://cureuphoria.com/activity.
When you try to “Comment” on any activity, you get this page: “http://cureuphoria.com/activity/reply/” and it displays the “Page not found. We’re sorry, but we can’t find the page that you’re looking for. Perhaps searching will help”, with the search form.
I tried to deactivate all the plugins and the problem is still there.
I use a sngle WordPress Version 3.2.1. – Buddypress 1.5.1.with a child theme, with only a few templates changed (header, footer, sidebar), and got a “functions.php” file in the child theme.
The problem is really annoying as nobody can comment on anyone activity.
Any help?