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Could not load file or assembly ‘Microsoft.ReportViewer.WebForms’

by | Jan 26, 2021

Are you stuck with ‘Could not load file or assembly ‘Microsoft.ReportViewer.WebForms’ error while restoring the Website? We can help you to fix it.

Usually, this error occurs when the ReportViewer files are not present in the bin folder.

At Bobcares, we often get requests to restore the site as a part of our Server Management Services.

Today, let’s see how our Support Engineers fix this error.


What is a Report Viewer?

The Microsoft Visual Studio includes report design functionality and this is controlled by ReportViewer.

ReportViewer is a freely redistributable control that enables embedding reports in applications developed using the .NET Framework and adds full-featured reports to custom applications.

Reports may contain tabular, aggregated, and multidimensional data. ReportViewer controls process the data and display the report in our application. The main benefits of the ReportViewer are given below.

  • It processes data efficiently – The ReportViewer can perform operations such as filtering, sorting, grouping, and aggregation by the reporting engine built into it.
  • It presents data in various ways such as lists, tables, charts, and matrices.
  • Similarly, we can specify fonts, colors, border styles, and background images in the report.
  • Also, it supports export to Excel, Word, and PDF formats.


How to fix Could not load file or assembly error?

Recently while restoring the website from the backup we got the below error message.

Could not load file or assembly ‘Microsoft.ReportViewer.WebForms, Version=, Culture=neutral, PublicKeyToken=89845dcd8080cc91’ or one of its dependencies. The located assembly’s manifest definition does not match the assembly reference. (Exception from HRESULT: 0x80131040)

Let’s see how our Support Engineers fix this error.

The error occurs when the ReportViewer files are not present in the bin folder. Therefore we fix the error by copying the files to the bin folder.

1. Initially, we go to the below location to access the Report Viewer files.

C:\Program Files (x86)\Microsoft Visual Studio 10.0\ReportViewer

The above path is the Microsoft Visual studio’s installation path and it can be different if we install it to another location.

2. Then we copy the below Report Viewer files to the bin folder.

  • Microsoft.ReportViewer.Common.dll
  • Microsoft.ReportViewer.WebForms.dll
  • Microsoft.ReportViewer.WinForms.dll
  • Microsoft.ReportViewer.WebForms.xml
  • Microsoft.ReportViewer.WinForms.xml

This will fix the problem and the site will load fine without any error messages.

[Still, have any queries on assembly error? – We can help you.]



In short, the Could not load file or assembly ‘Microsoft.ReportViewer.WebForms‘ error occurs when ReportViewer files are missing from the bin folder. In today’s writeup, we discussed how our Support Engineers fix this error easily.


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