Error faced in mail section

I have a form in my website,where i have an email field,While submtting the form An email should be sent to the mail address given in the form also a mail should be sent to the mail id which is statically given,

I tried doing this,but i faced the below error

Main mail: Mailer was unable to send mailCould not instantiate mail function.

The code which I used was,

[!downloadForm!][!eForm? &formid=`downloadForm` &to=`[+emailaddress+]` &tpl=`downloadForm` &thankyou=`downloadFormThankyou`!]

Could anybody help me on this