when you read the error message in full you may see that it refers to (in most cases) a Javascrpt error. Either the script is not compliant with your browser or the script has a bug or your browser does not support Javascript.
You may think the page works fine, but there are certainly items (pictures, forms, behavior) which do not work to the intentions of the creator of the page.
Just a simple explanation, you know these menu buttons with text on them. When you move your mouse over them, the colour changes, this is done with Java script.
With the new Netscape Navigator 6.x due in a few weeks (beta is released) the compatability between browsers will get better, programmers do not have to write different pages for individual systems etc.
Another example, with Java script I am able to determine which browser you are using, I can actually see which version you are using. Knowing this I am in the position to develop my page this way that I can define different layouts and behaviors for your actual screen resolution etc.
And if I develop something and your browser does not interpret this correctly, which indeed may happen due to a faulty datapackage you have received (without knowing of course) than you see the error.
If you are a friendly surfer you will copy the error and mail it to the webmaster of said site to investigate and rectify. Most important are the details, it shows lines, modules and so on. This is the only way to react from the programmers side.
Hope this was not too technical.
