Could not load file or assembly System.Data.SqlClient, Version= when I use System.Data.SqlClient Version 4.4.3


I use System.Data.SqlClient Version 4.4.3 for all .NET Standard 2.0 class libraries in my ASP.NET Core 2.0 project. Why do I get

Could not load file or assembly 'System.Data.SqlClient, Version=, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a'. The located assembly's manifest definition does not match the assembly reference. (Exception from HRESULT: 0x80131040)

when the project is published with VSTS to Azure App Service? And of course it perfectly works on my machine!

All this worked yesterday. But today I decided to update packages to:

<PackageReference Include="Microsoft.AspNetCore.All" Version="2.0.6" />
<PackageReference Include="Microsoft.VisualStudio.Web.CodeGeneration.Design" Version="2.0.3" />
asked on Stack Overflow Mar 22, 2018 by alvipeo • edited Mar 22, 2018 by alvipeo

6 Answers


Don't know whether this is the same situation that I faced. I added System.Data.SqlClient via nuGet and it worked fine.

answered on Stack Overflow Aug 2, 2018 by Watz

Downgraded to

<PackageReference Include="Microsoft.AspNetCore.All" Version="2.0.6" />

and everything works again! Lost 4 hours today!!!

answered on Stack Overflow Mar 22, 2018 by alvipeo

I got the same issue, SerializationException with message:

Unable to find assembly 'Microsoft.Data.SqlClient,  
March 3rd 2020 16:36:46Error
Version=1.0.19269.1, Culture=neutral, PublicKeyToken=23ec7fc2d6eaa4a5'

but everything is ok with dll, issue was caused by invalid connection string, it takes me almost few hours to figure out what happens!


This happens when some dependent assembly uses old version of same library. To solve that you can use assembly redirecting, to force old library use newer version.

put this in your app.config or in web.config in case of

    <assemblyIdentity name="System.Data.SqlClient"  publicKeyToken="b03f5f7f11d50a3a"  culture="neutral" />  
    <bindingRedirect oldVersion="" newVersion="" />  
answered on Stack Overflow Mar 22, 2018 by Davit Tvildiani

I had a similar issue to this today, I updated a number of packages including the All meta-package to 2.0.6. My app then wouldn't work quoting the error above. After a lot of investigation I did the following and it now seems to be working.

Connect to the Azure Web Site using FTP, navigate to the site -> wwwroot folder. Here I had a folder called "refs" and another called "runtimes". I deleted both of these folders (after taking a local backup), re-published my app and it worked!

Not sure why it worked but I thought this might be useful is someone stumbles across this with a similar issue.

answered on Stack Overflow Mar 24, 2018 by Adam Stapleton

For me, the solution was removing the System.Data.SqlClient package and installing it again. Doing the upgrade of the package wasn't sufficient.

answered on Stack Overflow Apr 9, 2018 by IronRod

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