ERROR: Throwing Microsoft.ReportingServices.ReportProcessing.ReportProcessingException: , Microsoft.ReportingServices.ReportProcessing.ReportProcessingException: Cannot create a connection to data source

I am migrating SQL Server 2008 R2 to new virtualized servers.  SQL Server and SSRS are on a single machine, so I do not think this is a double hop issue.  I am connecting to SSRS from a separate client machine.  I can see the reporting interface, so I know it gets to SSRS, but then it prompts me for a user name and password.  There is nothing in any Windows Event Log. Connections are authenticated Windows accounts.  If anyone has any idea...  I did not set SSRS up originally and have very little experience with it.

SSRS works fine in the test environment, but fails with the following error in production:

processing!ReportServer_0-6!f48!06/03/2013-09:52:37:: e ERROR: Throwing Microsoft.ReportingServices.ReportProcessing.ReportProcessingException: , Microsoft.ReportingServices.ReportProcessing.ReportProcessingException: Cannot create a connection to data source 'Database'. ---> System.InvalidOperationException: The ConnectionString property has not been initialized.
   at System.Data.SqlClient.SqlConnection.PermissionDemand()
   at System.Data.ProviderBase.DbConnectionClosed.OpenConnection(DbConnection outerConnection, DbConnectionFactory connectionFactory)
   at System.Data.SqlClient.SqlConnection.Open()
   at Microsoft.ReportingServices.DataExtensions.ConnectionExtension.Open()
   at Microsoft.ReportingServices.DataExtensions.SqlConnectionWrapperBase.Open()
   at Microsoft.ReportingServices.Diagnostics.DataExtensionConnectionBase.OpenDataSourceExtensionConnection(IProcessingDataSource dataSourceObj, String connectString, DataSourceInfo dataSourceInfo, String datasetName)
   --- End of inner exception stack trace ---;