Login failed for IUSR after IIS reinstallation

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I have Windows XP Pro SP3. I had to uninstall and reinstall IIS. The problem is that now I cannot connect to sql server 2000 from an asp page using the Internet Guest Account (IUSR) (although I changed nothing is the sql server settings, where the user ERICIUSR_ERIC is declared as a db_owner in my database). I am receiving this error:

Microsoft OLE DB Provider for SQL Server (0x80040E4D)
Login failed for user 'ERICIUSR_ERIC'.

But I AM able to connect to sql server using a username and a password.
In other words, this connection string works:

Provider=SQLOLEDB.1;Initial Catalog=MyDB;Data Source=.;User Id=MyUser;Password=MyPass;

and this does not work:

Provider=SQLOLEDB.1;;Initial Catalog=MyDB;Data Source=.Integrated Security=SSPI;Persist Security Info=False

What can I do to connect with the second connection string?

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I solved it using this:
You will need to remove and the re-insert the IUSR account back to SQL Server because after IIS was reinstalled, the new IUSR accounts will have a new SID.