You can also try contacting support here, or reading through the Open Tickets here (where you can see there are a bunch in about this issue).
EDIT: From finlee: [Another fix...]I figured out a way to fix this for now. I read about clearing your cache, but I have no idea what that is.
First, bring the pointer over you username – you should get a pull down menu of things including your profile, messages etc. If you don’t get the pull down message, you’ll have to go to a different page on LJ. I went to the bottom of the page and activated the “about” page.
Go back to your username and if you can see the pull down menu, go to your settings. When your settings page is open, click on the “Display” tab. The last option is “Design Version.” Click “ Set old design version” and then hit save. Your display will change.
Hit your “Friend’s feed” tab and you should be able to view everything and comment. You can always switch back to the newer version – there is a link on the right hand side that says “Switch to new version.”