PROBLEM:

When you try to run a report (or) Generate a model from an existing Data Source (or) Open a Model using Report Builder from the Report Server, you get the following error,

An attempt has been made to use a data extension 'SQL' that is not registered for this report server.

ROOT CAUSE:

One possible cause of this issue is that the registered SQL extension in your report server config file would have got modified / removed.

SOLUTION:

Open RsReportServer.config file located under <installation path of reporting service> / reportserver folder.

Locate the element,

And make sure it is there as below,

<Extensions> <Data>

<Extension Name="SQL" Type="Microsoft.ReportingServices.DataExtensions.SqlConnectionWrapper,

Microsoft.ReportingServices.DataExtensions"/>

<SemanticQuery>

<Extension Name="SQL" Type="Microsoft.ReportingServices.SemanticQueryEngine.Sql.MSSQL.MSSqlSQCommand,

Microsoft.ReportingServices.SemanticQueryEngine">