In addition to what Mahain already said..I would also put null check as follows
if (crmForm.all.companyname.DataValue!=null) { crmForm.document.title=crmForm.all.companyname.DataValue; }
Hi,
you can set crm form tiltle using "crmForm.document.title" so if you want to set companyname to it you can use this like
crmForm.document.title=crmForm.all.companyname.DataValue; //Just paste this line on lead form onload