Yahoo!Mail - Cannot reply/forward or auto-complete. only on YAHOO mail. can't even get to "use plain text"

Same here, started a few hours ago - but i get it all jumbled and corrupted, but i also cannot change back to old version email and cannot even contact Yahoo to let them know. Also am able to use all other Yahoo services

Not just java, but javascript. Open up your Internet Options (if you're using IE) and make sure you have scripting enabled. Otherwise, none of the features on the site will work. But, yes, it could be a temporary problem in which you aren't able to receive the scripts for the page to work, in which case just check back later.

I am having exactly the same problem (as are many other people). I had changed nothing on my computer, did the JAVA update, have all the right "scripting" choices enabled, etc. My error code shows "object expected", but that doesn't give me any more clues I'm afraid. I originally had suspected it was linked to an "automatic" update that came through my computer, but others have told me they don't get updates automatically and they are having the same problem. Yahoo is (no doubt) being deluged with questions, but so far has produced no answers. I provided them with all of the details of my system for research, hopefully if everybody does the same, they will find the link and the way to solve the problem.