Issue: The report definition has an invalid target namespace 'http://schemas.microsoft.com/sqlserver/reporting/2016/01/reportdefinition' which cannot be upgraded

So , when we try to use old rdlc report with new reporting services. We often face this error. We cannot solve this issue just by change the reporting namespace in xml as that will change automatically the next time you will make any change in the report. So for fixing the issue, we have to make sure our old report is compatible with the new reporting services. For this, We have to install the nuget package

'Microsoft.ReportingServices.ReportViewerControl.WebForms' version="140.340.80"

You can check the correct package and version number in the image below. After installing the package try to run the rdlc report and this time you will not face the same error.

So, this is how you can solve the issue The report definition has an invalid target namespace 'http://schemas.microsoft.com/sqlserver/reporting/2016/01/reportdefinition' which cannot be upgraded in rdlc report.