Please open the folder where the Telerik.ReportDesigner(.x86).exe resides and remove any external assemblies. Then try to start the again teh EXE.
If the Standalone Designer is started correctly, inspect the removed thrid-party assemblies and if they have references to different version of Telerik Reporting or Telerik UI for WPF. The Standalone Report Designer uses Telerik Reporting and Telerik UI for WPF which may causes assembly version conflicts.
If the Standalone Report Designer fails to open, test re-installing or upgrading the product. Note that the machine must cover Telerik Reporting system requirements
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