We all are using update panel for the Ajax implementation in every site. Nowadays Ajax is almost there in each and every site. Update panel is working fine with the all other controls but when we use the file upload control then its not working fine. I have searched from lots for this and i have found one of simple solution from the Imran's blog. It is so simple and works very well. You just need to add the "multipart/form-data" attribute to the form.
Here is the link from which you can have all the information.
Thanks Imran for posting nice info like this.