There is a permission problem:
- Execute "dcomcnfg"
- Open Component Services > Computers > My Computer > DCOM Config
- Search for "Microsoft Excel Application"
- Right-Click on it and open the properties
- if not exists run "excel.exe -regserver"
- Choose "Identity" tab
- Normally this is set to "the launching user". You have to change this to "the interactive user" or a admin user of your choice.
- Apply these new settings and test your COM application. It should work fine now.
I got it from the comments here: http://www.php.net/manual/en/class.com.php