Is anyone familiar with Easymail

The following code keeps bringing up error code 24

smtp=createobject("EasyMail.SMTP.5")
smtp.mailserver=strserver
smtp.FromAddr=strfrom
smtp.bodyencoding=0
smtp.addrecipient("",strto,1)
smtp.subject=strsubject
smtp.bodytext=strbodytext
smtp.addattachment("x:\swissglob\pods\podprob.doc",0)
smtp.licensekey="colin northway (Single Developer)/00A0530510931E004C00"
smtp.timeout=240
ddrx=smtp.send()

ddrx always contains error code of 24 - does anyone know what could be the cause