Just to verify, you are trying to create an app in the developer area of Twitter, but you are getting an error when trying to save/create it? If that's the case, we've never heard of that error before. I would suggest trying from another browser to see if this helps; for instance, I was just able to create a test app in Chrome with no issues, so maybe try Chrome.
If that's not the problem you're having, please clarify.
Thanks
-Melissa