htmlfile: Uknown runtime error

[scrupul0us]

im getting the following error:

htmlfile: Unknown runtime error

on this code:

[code]function letterhead(mode)
{
    if (mode=='off')
    {
    html_header = document.getElementById("form_header").innerHTML;
    html_footer = document.getElementById("form_footer").innerHTML;
    document.getElementById("form_header").innerHTML = "<div style=\"height:1.75in; width: 7.5px;\"></div>";
    document.getElementById("form_footer").innerHTML = "<div style=\"height:1in; width: 7.5px;\"></div>";
    document.getElementById("letterheadmode").innerHTML = "<a href=\"#\" onclick=\"letterhead('on')\">Add Letterhead</a>";
    }
    if (mode=='on')
    {
    document.getElementById("form_header").innerHTML = html_header;
    document.getElementById("form_footer").innerHTML = html_footer;    
    document.getElementById("letterheadmode").innerHTML = "<a href=\"#\" onclick=\"letterhead('off')\">Remove Letterhead</a>";
    }
}[/code]

on:

[code]
document.getElementById("form_header").innerHTML = "<div style=\"height:1.75in; width: 7.5px;\"></div>";[/code]