I'm sure for blogger who love to spend most of their time tweaking their blog layout are very familiar with this error code. I myself have experience many times when tried to edit the css n xml. And the best part is..when you see this error page once, it will keep continue showing the same thing no matter what you do. Even if you upload the template that you've back up earlier, re-code the whole thing, or even copy paste the valid code from your text editor...still, same error message will appear. I'm not sure whether this bug only appears in a particular web browser or happens to all web browser, but at that time i was using my firefox. Luckly there so many nice people out there in the internet are willing to share their experience and give solution..i manage to fix the problem then. And now i'm passing you the information

All you need to do is:
1. Close your mozilla
2. Open other browser such as safari or ie
3. Go to layout and click the edit html link
4. Re upload the template file that save earlier (since that you play a lot with the layout I assume you already backup the template file..)
5. !!! problem fix and you can get back to your firefox for your blogging routine.

Hope this helps..:)