Microsoft Knowledge Base Article 843093 contains the following summary:
Microsoft Exchange Server 2003 and Microsoft Exchange 2000 Server use Microsoft Internet Information Services (IIS) to provide support for Exchange-related services. IIS stores its configuration settings in the IIS metabase. The metabase is a database that resides in memory on the computer that is running IIS. When the computer shuts down, all the metabase settings are written to a file that is named Metabase.bin.
If the metabase becomes corrupted, your Exchange environment may become unstable, or Exchange-related services may not start.
You can use several metabase editing tools to view keys in the metabase or to export or import metabase settings. Additionally, you can use these tools to determine whether the problem that you experience occurs because of metabase corruption.
This article describes how to troubleshoot IIS metabase corruption issues that you may experience on your computer that is running Exchange Server 2003 or Exchange 2000 Server.