The "Format of the initialization string does not conform to specification starting at index 0" error message is usually shown when the configuration file of the application does not contain the required named connection string. For more information please check the Connection Strings and Configuration Files MSDN page.
When the reports get rendered in a web application, the configuration file is the corresponding Web.config file. In the Report Designer, the Reporting engine is running in the context of the designer application, hence it is necessary to register the connection string in its configuration file:
- In the case of Visual Studio designer, this is the App.config file of the corresponding ReportLibrary project.
- In the case of Standalone designer, this is the Telerik.ReportDesigner.exe.config file that can be found in the folder where the designer executable file is deployed - by default (Telerik Reporting installation folder)\Report Designer.
For more information, please, refer to Configuration article.
Please check the configuration file and make sure that the named connection string used in the report definition exists there.
In case the issue persists, please open a new support ticket and send us a runnable sample project exhibiting the issue, so we can review it locally and advise accordingly.
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