Error in creating Excel Object : Retrieving the COM class factory

You might have faced a problem while creating an object of MS Excel using

Excel.ApplicationClass xl = new Excel.ApplicationClass();

resulting in the following error.

Retrieving the COM class factory for component with CLSID {00024500-0000-0000-C000-000000000046} failed due to the following error: 80070005.

Possible reasons for it are that your ASPNET account doesnt have enough permissions to create that COM object so you have to grant permissions to the user which is accessing that COM object.

By default ASP.NET web applications run under the \ASPNET account, if you are using impersonation than the \IUSR_ is used to run that application so in each case you have to grant permissions to the respective users

You can grant permissions to those accounts to access the COM object on Windows XP using the following steps:

Configure DCOM

• 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
• Select the Security Tab

• Under "Launch and Activation Permissions" select the "Customize" option.
• Click the "Edit" button
• • Click the "Add" button to add a new account to the list.
  • On the dialog that is displayed click the Locations button
    
    (select the first item which is your computer name)
    
    

• Click the OK button
• On the dialog that is displayed enter "ASPNET" as the account name (make sure location is set to the name of the computer that IIS is on) onWindows XP
• On the dialog that is displayed enter "IUSR_" as the account name if you are using impersonation (make sure location is set to the name of the computer that IIS is on) onWindows XP

• Click the OK button
  
• Now make sure you select the following options for the "ASP.NET Machine Account" or the account that is the application pool identity ( by default Network Service)
  
  • Local Launch : Allow
  • Remote Launch : [blank]
  • Local Activation : Allow
  • Remote Activation : [blank]

Click the OK button and test your web application again and it should work fine.

The above steps have been taken from the following URL and you can go through it for a more detailed walk through

http://blog.crowe.co.nz/archive/2006/03/02/589.aspx