A. VMware reports in knowledgebase article 1026688 that corrupted virtual machine (VM) entries in the vCenter database can cause the vCenter Server to fail after upgrading to vCenter Server 4.1.
In that same article, VMware provides two scripts—one for SQL Server and another for Oracle—that will perform a series of queries on a vCenter Server database. The result of those queries will identify where any corrupted VM data has been found in the database.
If any corrupted VM data is found, those VMs must be powered down and removed from the vCenter Server inventory before upgrading to 4.1. Once upgraded, the VMs can be added back to the database and powered on again. These scripts must run without finding corrupted data if the upgrade is to proceed successfully.
If you've already upgraded your vCenter Server to 4.1 and received this error, you need to downgrade the server back to 4.0 prior to performing any of the steps noted above.