Could not load file or assembly 'Microsoft.VisualStudio.Web.PageInspector.Loader

Question 1

I just ran into the same problem, and the culprit was my uninstalling of Visual Studio Express 2012. It's possible that it might be any version of Visual Studio, as comments on this answer are indicating the issue still happens with Visual Studio 2019. My overall order of operations was:

Installed Visual Studio Express 2012 (long time ago)
Used Visual Studio Express 2012 happily for many months
Installed Visual Studio 2013 Premium
Used Visual Studio 2013 Premium happily for weeks
Uninstalled Visual Studio Express 2012
ERROR

I'm not 100% certain on the cause of it, or what combinations of Visual Studio versions would exhibit this behavior. But the solution for me was to edit the root web.config files in the framework directories:

C:\Windows\Microsoft.NET\Framework\v4.0.30319\Config\web.config
C:\Windows\Microsoft.NET\Framework64\v4.0.30319\Config\web.config

(For different framework versions you may have different folders.)

And remove the nodes:

<remove assembly="Microsoft.VisualStudio.Web.PageInspector.Loader, Version=1.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" />
<add assembly="Microsoft.VisualStudio.Web.PageInspector.Loader, Version=1.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" />

Be careful not to remove any opening/closing parent nodes which are also on the same line(s) as these.

This resolved the issue for me.

Question 2

No need to remove those lines
Just close and reopen the Visual studio with Admin privileges.

Question 3

I got the same problem but not on my development machine but on hosting server.

C:\Windows\Microsoft.NET\Framework\v4.0.30319\Config\web.config C:\Windows\Microsoft.NET\Framework64\v4.0.30319\Config\web.config

I was able to fix it by adding below code to my web.config

<compilation targetFramework="4.5"> 
    <assemblies> 
        <remove assembly="Microsoft.VisualStudio.Web.PageInspector.Loader,
    Version=1.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" />
    </assemblies> 
</compilation>

or by removing reference to this assembly from web.config files in framework directories.

I never installed VS there and i never had PageInspector installed there. Any idea why those configs reference them?

Question 4

Update: fixed in Visual Studio 2019 Version 16.0.3 according to this page.

If this happens after upgrading to Visual Studio 2019 RC, the following workaround helped:

Find the download cache directory
Use Explorer or better to find the AspNetDiagnosticPack.msi within this directory.
Run (double-click) the AspNetDiagnosticPack.msi file (this will force the installation of this MSI).

Workaround found here

Question 5

I had this issue after installing Visual Studio 2019 (whilst 2017 was still installed). It's caused by a missing component - AspNetDiagnosticPack.msi - that fails to install a required package into C:\ProgramData\Microsoft\VisualStudio\Packages\

The solution that worked for me was this:

Close Visual Studio
Download the package from:

https://download.visualstudio.microsoft.com/download/pr/e13d544f-5a3c-4bb3-9a7c-1e56b1f90e10/f8e5888ff01a7009ef8c2ef16aa02ab9/aspnetdiagnosticpack.msi

Run the installer and install.

This should fix it.

More information can be be found: https://developercommunity.visualstudio.com/content/problem/398640/could-not-load-file-or-assembly-microsoftvisualstu-7.html

Question 6

For those who might end up here, try removing the following line in the Web.Config file of your Project while debugging <identity impersonate="true" userName="blah" password="blah">

It took time until I finally came across the following thread: Could not load file or assembly or one of its dependencies. Access is denied. The issue is random, but after it happens once, it continues

Question 7

I've ran into this error while trying to run an ASP.NET project in VS2013 after having uninstalled a VS2015 preview. Repairing the VS2013 installation seems to have solved the problem.

Question 8

I got this answer is perfect for me

No need to remove those lines

Just close and reopen the Visual studio with Admin privileges.

Question 9

I removed the dll from gac and it started working. I am not sure where those dlls came from. If you have 2 or more versions of visual studio, reinstall the last version.

Question 10

Try updating your Microsoft.ApplicationInsights nuget package. This also installs other dependencies. I ran into this problem when I had to change my Target Framework.

Tools > NuGet Package Manager > Manage NuGet Packages for Solution...
search for "applicationinsights"

or run

Install-Package Microsoft.ApplicationInsights

Question 11

Had a similar problem (another assembly) and for me it was a missing line in the web.config on the machine. A line that I think lets the web server load (any?) dll. I had to add "*" to the compilation-assemblies list in the web.config:

C:\Windows\Microsoft.NET\Framework64\v4.0.30319\Config\web.config

Like this

    <compilation>
      <assemblies>
        ...
        <add assembly="*" />
      </assemblies>
    </compilation>

To find it I had to compare the file with one from a working server. So it seems to me that It really is a load failure, but to determine why it fails, we need to be Sherlook H.. Normally I use a tool like ProcessMonitor to find out why I get a Load Failure, but this time, of course, it gave me no useful output.. IIS never tried to load the assembly!

Question 12

If you don't see web.config in both of paths: C:\Windows\Microsoft.NET\Framework\v4.0.30319\Config\web.config C:\Windows\Microsoft.NET\Framework64\v4.0.30319\Config\web.config

file "Web" is in "C:\Windows\Microsoft.NET\Framework64\v4.0.30319\Config\" what I really want to show you, It's Web.config, you should open it with: notepad++... and remove:

//<remove assembly="Microsoft.VisualStudio.Web.PageInspector.Loader,
    Version=1.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" />"

I finish my problem with them.

Question 13

Our project had (incorrectly) reference to the PageInspector.Loader.dll in the GAC for a long time:

 <ItemGroup>
    <Reference Include="Microsoft.VisualStudio.Web.PageInspector.Loader">
      <HintPath>..\..\..\..\..\..\Windows\Microsoft.NET\assembly\GAC_MSIL\Microsoft.VisualStudio.Web.PageInspector.Loader\v4.0_1.0.0.0__b03f5f7f11d50a3a\Microsoft.VisualStudio.Web.PageInspector.Loader.dll</HintPath>
    </Reference>
  </ItemGroup>

It worked for some time, but recently deployment to Azure caused the error "Can not find compilation library location for package Microsoft.VisualStudio.Web.PageInspector.Loader".

We found and deleted the reference from .csproj file and the problem was fixed.

Question 14

I opened today a 10 year old project and encounter this issue in VS 2019 (16.9.1), in my case it was

<trust level="Medium"/>

removing above line from the web.config or setting <trust level="Full"/> solved this issue.

Question 15

I know this is an old one but I ran into this error when debugging with Visual Studio 2010 (I also run 2013, 2017 and 2019 on the same machine...I have a few legacy apps :oP). In my case, I debug using local IIS as webserver (not express) and I ended up having to recycle the websites Application Pool which did the trick to clear the error (after restarting 2010). Dave

Question 16

it solved the problem on at my end by applying the approved solution in this thread.

modifying the following two files, and removing Microsoft.VisualStudio.Web.PageInspector.Loader resolved the issue.

C:\Windows\Microsoft.NET\Framework\v4.0.30319\Config\web.config
C:\Windows\Microsoft.NET\Framework64\v4.0.30319\Config\web.config