Powershell, excel 2003 and 'type library' exception

I have written some simple powershell script:

$excel = New-Object -com Excel.Application
$excel.Workbooks.Open("C:\temp\mybook.xls")

It runs OK in on PC.

However, when my colleague runs it, he gets this exception

    Old format or invalid type library. (Exception from HRESULT: 
0x80028018 (TYPE_E_INVDATAREAD))

What does this error message mean?