Symptoms
On server that is running Microsoft SQL Server 2008 Reporting Services, you generate a report from a custom data extension data source. To do this, you use the “Asynchronous Processing = True” setting in the connection string property.When you run the report, the report server stops responding.
Resolution
This issue occurs because the System.Data.SQLclient namespace does not support asynchronous processing in any hosted common language runtime (CLR) environment. Because Reporting Services hosts the CLR within the Reporting Services process, the asynchronous call always fails.
Note The System.Data.SQLclient namespace is the SQL Server .Net Data Provider.