well, if u r using firefox, try this:
install the
add n edit cookies extension.
restart firefox and log into ur rediff account. now, go to tools>cookie editor. in the window that pops, scroll down to the rediff.com cookies and click on edit. now, set a new expiration time for the cookies, say a month ahead.
i dont know if this will work for sure, but i use it to edit cookies for forums so that i dont have to log in everytime.