Use Cookie-free Domains for Components

This is an excerpt from Yahoo Best Practices for Speeding Up Your Web Site

When the browser makes a request for a static image and sends cookies together with the request, the server doesn’t have any use for those cookies. So they only create network traffic for no good reason. You should make sure static components are requested with cookie-free requests. Create a subdomain and host all your static components there.
If your domain is www.example.org, you can host your static components on static.example.org. However, if you’ve already set cookies on the top-level domain example.org as opposed to www.example.org, then all the requests to static.example.org will include those cookies. In this case, you can buy a whole new domain, host your static components there, and keep this domain cookie-free. Yahoo! uses yimg.com, YouTube uses ytimg.com, Amazon uses images-amazon.com and so on.
Another benefit of hosting static components on a cookie-free domain is that some proxies might refuse to cache the components that are requested with cookies. On a related note, if you wonder if you should use example.org or http://www.example.org for your home page, consider the cookie impact. Omitting www leaves you no choice but to write cookies to *.example.org, so for performance reasons it’s best to use the www subdomain and write the cookies to that subdomain.

Ref: Please read here

This is a common Asp.Net error when updating List Box items on the client side.
I asked this question on stackoverflow.com (Click here).

Just reflecting on how many views people have had on this question, it seems to be a common issue most Asp.Net developers encounter.

Follow some good work being done to teach Kids programming. Click here
The teaching material is all free!!!

An excellent article on the Asp.Net application and page life cyle. Please click here