User839733648 posted
Hi nattikomatti,
You could try to remove the reference dll and any assemblies entry of ReportViewer from web.config.
Then add new reference of ReportViewer and rebuild the project.
Or you may try to compare between <%@ Register Assembly="Microsoft.ReportViewer.WebForms, Version=11.0.0.0 and the version that is written in the reference you added in the web.config file.
If there is a difference in version of the Microsoft.ReportViewer.WebForms then change as per the version installed in the server.
For more, you could refer to : https://stackoverflow.com/a/30173426/10487763
Best Regards,
Jenifer