subscribe widget only works if logged in


I have a strange problem with subscribe by email plugin widget.

When someone enter their email address and submit it should send them a confirmation email but in my case it doesn't work that way. it shows the confirmation message but does not actually send any email.

However I noticed that if I am logged in as a admin, the widget just works fine.

I am using it here:
the website is in a indian language but you will be able to see the widget in left sidebar on top.