Upload image twice using Ajax control toolkit

I use Ajax Control Toolkit's AsyncFileUploader control to allow user to upload image files.

However I encountered a strange problem and that is, if I try to upload the same image twice (ba开发者_运维技巧ck to back) it does not upload. [I guess this is due the fact that the uploaded files are stored in user's session]

Also, I would like to have the contents of Upload textbox cleared once the file is uploaded.

Thanks :)