Wrong version of .NET assembly getting copied to Web Forms bin directory


I'm working on an ASP.NET Web Forms web site and frequently get run-time exceptions like the following:

Could not load file or assembly 'Newtonsoft.Json, Version=, Culture=neutral, PublicKeyToken=30ad4fe6b2a6aeed' or one of its dependencies. The located assembly's manifest definition does not match the assembly reference. (Exception from HRESULT: 0x80131040)
=== Pre-bind state information ===
LOG: DisplayName = Newtonsoft.Json, Version=, Culture=neutral, PublicKeyToken=30ad4fe6b2a6aeed
LOG: Appbase = file:///C:/Code/MyProject/
LOG: Initial PrivatePath = C:\Code\MyProject\bin
Calling assembly : System.Net.Http.Formatting, Version=, Culture=neutral, PublicKeyToken=31bf3856ad364e35.
LOG: This bind starts in default load context.
LOG: Using application configuration file: C:\Code\MyProject\web.config
LOG: Using host configuration file: \\foo\bar\Profile.v2\simonm\Documents\IISExpress\config\aspnet.config
LOG: Using machine configuration file from C:\Windows\Microsoft.NET\Framework\v4.0.30319\config\machine.config.
LOG: Redirect found in application configuration file: redirected to
LOG: Post-policy reference: Newtonsoft.Json, Version=, Culture=neutral, PublicKeyToken=30ad4fe6b2a6aeed
LOG: Attempting download of new URL file:///C:/Users/simonm/AppData/Local/Temp/Temporary ASP.NET Files/vs/8d6ca9e7/1d38a78a/Newtonsoft.Json.DLL.
LOG: Attempting download of new URL file:///C:/Users/simonm/AppData/Local/Temp/Temporary ASP.NET Files/vs/8d6ca9e7/1d38a78a/Newtonsoft.Json/Newtonsoft.Json.DLL.
LOG: Attempting download of new URL file:///C:/Code/MyProject/bin/Newtonsoft.Json.DLL.
WRN: Comparing the assembly name resulted in the mismatch: Major Version
ERR: Failed to complete setup of assembly (hr = 0x80131040). Probing terminated.

They're invariably because the "wrong" version of an assembly (it always seems to be Newtonsoft.Json) gets copied to the Bin directory despite the fact that the packages.config in the root of the site has:

<package id="Newtonsoft.Json" version="11.0.2" targetFramework="net45" />

and the web.config contains:

<assemblyIdentity name="Newtonsoft.Json" publicKeyToken="30ad4fe6b2a6aeed" culture="neutral" />
<bindingRedirect oldVersion="" newVersion="" />

Can somebody please explain what dictates which assembly gets copied to the Bin directory, why this keeps happening and how to prevent it from happening in the future?

asked on Stack Overflow Mar 18, 2019 by Simon Morgan

2 Answers


I guess, that some of your used frameworks/libraries are using different versions of Newtonsoft.Json. First, check your frameworks/libraries if they are requiring different versions of the Newtonsoft.Json library.

When you detected which is the (minimum) required version of Newtonsoft.Json try to reinstall this version through Nuget.

answered on Stack Overflow Mar 18, 2019 by Marvin Klar

This seems to be cause by a number of factors, but ultimately boils down to having a .refresh file in the Bin directory that points to a different version of the assembly than the one referenced in the web.config.

It looks like these .refresh files get added when you (either manually or automatically due to e.g. Update-Package) add a reference to an ASP.NET project. If you look at the contents of a .refresh file, it's just the path to a .dll file. When you build, MSBuild (I assume) checks whether the Foo.dll in your Bin directory matches the one referenced by Foo.dll.refresh and, if they don't, copies the one referenced by the .refresh file into your Bin.

I think this combined with switching branches in Git to one that has a reference to a different version referenced in the web.config combined with the .refresh files not being in version control is what causes these problems.

answered on Stack Overflow Nov 11, 2020 by Simon Morgan

User contributions licensed under CC BY-SA 3.0