Classic report layout not available from RTC under SQL Server 2008

It is well known that you can run a report with a classic layout from the RTC of NAV 2009.
(see the online help “How to: View Classic Report Layouts from the RoleTailored Client”, e. g.)
The main things you have to pay attention to is to enable TCP/IP protocol on the SQL Server and eventually delete the RTC layout of the report.
This all works fine on the SQL Server 2005 running with a standard SQL Server instance.

But if I try to run a classic layout from the RTC under SQL Server 2008, I get an error message from the RTC:
“The supplied servername is not valid”, together with an event protocol entry, which I provide in extracts:

Event ID: 0

Type: Microsoft.Dynamics.Nav.Types.Exceptions.NavNCLArgumentException
Message: The supplied server name is not valid.
at Microsoft.Dynamics.Nav.Client.ConnectionStateManager.CallServer[T](CallServerMethod1 callServerMethod) at Microsoft.Dynamics.Nav.Client.ServerInvocationHandler.CallServer[T](CallServerMethod1 callServerMethod)
at Microsoft.Dynamics.Nav.Client.ServiceConnectionBase.CallServer[T](CallServerMethod`1 callServerMethod)
at Microsoft.Dynamics.Nav.Client.ServiceConnection.ActionField(NavRecordState& state, NavDataSet recDataSet, String controlTriggerMethodName)
at Microsoft.Dynamics.Nav.Client.DataBinder.NSTDataAccess.ActionMethod(String triggerName)
at Microsoft.Dynamics.Nav.Client.Actions.InvokePageTriggerAction.InvokeTrigger(LogicalControl logicalControl, UISession uiSession)
at Microsoft.Dynamics.Nav.Client.Actions.InvokePageTriggerAction.InvokeCore(Boolean async, LogicalControl logicalControl, Object state, UISession uiSession)
at Microsoft.Dynamics.Framework.UI.Action.InvokeCoreWithErrorHandling(Boolean async, LogicalControl logicalControl, Object state, UISession uiSession)
Source: Microsoft.Dynamics.Nav.Client.ServiceConnection

Could this be a problem arising from the use of SQL Server 2008?
Can anybody else run a classic report layout from the RTC with SQL Server 2008?

The problem may not be the SQL Server version but instead the use of a named SQL Server instance instead of a standard instance.
This is suggested here: