Clicking on the replies tab in twitter will return a pop-up,
"Twitter is stressing out a bit, so this feature is temporarily disabled".
One benefit has been the use of summize which provides a much richer experience. All you need to do is type your twitter name into the summize searchbox with the @sign in front. If you don't put the @sign in front, then you will see your own tweets. This is equivalent to the archive tab on twitter, which does work. Not only does summize work, but I think it works better than twitter. It finds your name, even when it is placed in a series of names which twitter has trouble with. Also, I realized that many times your name is misspelled in a reply and you can find these situations very easily with summize which you couldn't find in twitter. For example, I found the following misspellings of my simple twitter name, warrenss:
Have you ever tried that?--you may be surprised. Hopefully the replies tab will be working soon, but in the interim, take advantage of the summize features.