If you run the service using Network Service Account then you need to add permission to Microsoft Excel COM Object because by default Microsoft Excel as a COM object can only activated by the following accounts:
- Go to the Start-Run menu item.
- Type in "DCOMCNFG" and hit enter.
- This should load the "Component Services" MMC (you can also load from Administrative Tools - Component Services"
- Expand "Component Services"
- Expand "Computers"
- Expand "My Computer"
- Select the "DCOM Config" item
- Select the "Microsoft Excel Application" item.
- Right click and select Properties
- Add Permission to network service or ASP Net account