Problems with mail functions.

I am having issues with sending mail. I have contacted the provider  
and according to them they recommend using the mail function built  
into php. I am finding though that when I have mail set as my mailer  
option I get the following error.

Below if the error message I receive when I try to send a test  
message. I am using the mail module' Version 0.1.1  2005-11-02'

Function failed

The message was not sent. Mailer Error: Could not instantiate mail  
function.
Explanation:

The function executed correctly, but the result was a failure.
Stack:

      at mail_adminapi__sendmail(_sendmail.php:322)
      at xarmodapifunc(xarMod.php:997)
      at mail_adminapi_sendmail(sendmail.php:176)


Array
(
     [0] => 2
     [1] => FUNCTION_FAILED
     [2] => systemexception Object
         (
             [msg] => The message was not sent. Mailer Error: Could  
not instantiate mail function.
             [id] => 0
             [major] => 0
             [defaults] =>
             [title] =>
             [short] =>
             [long] =>
             [hint] =>
             [stack] => Array
                 (
                 )

             [product] => App - Core
             [component] => Mail
             [module] => mail
         )

)


      at xarmodapifunc(xarMod.php:997)
      at mail_admin_sendtest(sendtest.php:71)


Array
(
     [0] => Array
         (
             [info] => [email protected]
             [name] => Admin
             [recipients] => Array
                 (
                 )

             [ccinfo] =>
             [ccname] =>
             [ccrecipients] => Array
                 (
                 )

             [bccinfo] =>
             [bccname] =>
             [bccrecipients] => Array
                 (
                 )

             [subject] => test43
             [message] => iliglg g 8g giug ipug ipg ig iugb oyulg  
uyolf<br />

             [htmlmessage] => iliglg g 8g giug ipug ipg ig iugb oyulg  
uyolf<br />

             [priority] => 3
             [encoding] => 8bit
             [wordwrap] => 78
             [from] => [email protected]
             [fromname] => Admin
             [usetemplates] => 1
             [when] => 0
             [attachName] =>
             [attachPath] =>
             [htmlmail] =>
         )

)


      at xarmodfunc(xarMod.php:886)


Array
(
     [0] => mail
     [1] => admin
     [2] => _sendmail
     [3] => Array
         (
             [info] => [email protected]
             [name] => Admin
             [recipients] => Array
                 (
                 )

             [ccinfo] =>
             [ccname] =>
             [ccrecipients] => Array
                 (
                 )

             [bccinfo] =>
             [bccname] =>
             [bccrecipients] => Array
                 (
                 )

             [subject] => test43
             [message] => iliglg g 8g giug ipug ipg ig iugb oyulg  
uyolf<br />

             [htmlmessage] => iliglg g 8g giug ipug ipg ig iugb oyulg  
uyolf<br />

             [priority] => 3
             [encoding] => 8bit
             [wordwrap] => 78
             [from] => [email protected]
             [fromname] => Admin
             [usetemplates] => 1
             [when] => 0
             [attachName] =>
             [attachPath] =>
             [htmlmail] =>
         )

)


      at xarmain(index.php:91)