Compilation Error (Website Not Recognizing .NET 4.5) - compilation

Question

I am trying to get a website to recognize a new version of .Net (4.5) so that I can upgrade to the final version of DNN (7.2). I have .Net 4.5 installed but when I go into the IIS settings, switch the framework to 4.5 (it actually says 4.0 bc the version is technically 4.03), and then refresh local host I get the error:
"Compilation Error
Description: An error occurred during the compilation of a resource required to service this request. Please review the following specific error details and modify your source code appropriately.
Compiler Error Message: CS1703: An assembly with the same identity 'System.Web.Extensions, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35' has already been imported. Try removing one of the duplicate references.
[No relevant source lines]"
Haven't found anything useful thus far on the web regarding this. Please Help!
Update: the version referenced in the web.config does say 3.5.0.0 Is this the issue?

Answer 1

Your website only needs to be configured to use .Net 4.0
.Net 4.5 is an extension of the version 4.0.
Depending on the method you use to switch from .Net 2.0 to .Net 4.0, you would have to replace references to version 3.5 by references to version 4.0 in your web.config.

Answer 2

I was moving a dnn site from SSMS 2008 to 2012 to upgrade a DotNetNuke 4.8.0 site to 5.4.0 (I know it's old and that it's 5.4 and stable, I can continue the upgrade path) and came across the Compiler Error Message.
Compiler Error Message: CS1703: An assembly with the same identity
'System.Web.Extensions, Version=4.0.0.0, Culture=neutral,
PublicKeyToken=31bf3856ad36e35' has already been imported. Try
removing one of the duplicated references.
I replaced two references to 3.5 to 4.0 in web.config and it fired right up after I replaced the old core files with the 5.4 upgrade files.

Answer 3

I had a similar build error:
An assembly with the same identity 'System.Runtime, Version=4.0.0.0,
Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a' has already been
imported. Try removing one of the duplicate references.
The problem was with <assemblyBinding> in web.config. I had to change
<runtime>
<assemblyBinding xmlns="urn:schemas-microsoft-com:asm.v1">
<dependentAssembly>
<assemblyIdentity name="System.Runtime" publicKeyToken="b03f5f7f11d50a3a" culture="neutral" />
<bindingRedirect oldVersion="0.0.0.0-2.6.10.0" newVersion="2.6.10.0" />
</dependentAssembly>
</assemblyBinding>
</runtime>
To (note the binding redirect versions)
<runtime>
<assemblyBinding xmlns="urn:schemas-microsoft-com:asm.v1">
<dependentAssembly>
<assemblyIdentity name="System.Runtime" publicKeyToken="b03f5f7f11d50a3a" culture="neutral" />
<bindingRedirect oldVersion="0.0.0.0-4.0.0.0" newVersion="4.0.0.0" />
</dependentAssembly>
</assemblyBinding>
</runtime>
I think the original assembly binding redirect was added when I upgraded the site from asp.net 2.0 to 4.0. For some reason this worked on one of my machines but when I checked out the project on another machine the build failed.

Answer 4

In my case, I've installed something from Nuget (Humanizer) and it created a folder in my web site called packages where it added new references to basically every knwon .net class (it seems that it needed to resolve some dependencies - a lot of dependencies!! :)) ), that is why I had multiple references to a lot of .net classes. I've removed that package entirely and it removed with it all other dependency references.
Now all is ok.. thank God! :)