"This assembly is built by a runtime newer than the currently loaded runtime and cannot be loaded"

I'm getting the error: "This assembly is built by a runtime newer than the currently loaded runtime and cannot be loaded."

I have a .NET 4.0 dll project that is being called by a .NET 2.0 project. Is there a way to reconcile the difference in framework?

Solution 1:

I have a .NET 4.0 dll project that is being called by a .NET 2.0 project. Is there a way to reconcile the difference in framework?

Not that way round, no. The .NET 4 CLR can load .NET 2 assemblies (usually - there are a few exceptions for mixed-mode assemblies, IIRC), but not vice versa.

You'll either have to upgrade the .NET 2 project to .NET 4, or downgrade the .NET 4 project to .NET 3.5 (or earlier).

Solution 2:

If you have already tried all the other logical solutions on this page, then double check this. In my app.config I had a reference to an old framework.

<startup>
  <supportedRuntime version="v2.0.50727"/>
</startup>

should have been

<startup>
  <supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.0"/>
</startup>

The project tab correctly showed v4.0 but the app.config was not committed to our repo with that change. To fix it, I changed the framework to something else and back to 4.0 again, which updated my app.config file.

Solution 3:

I got same error message. I was giving

C:\WINDOWS\Microsoft.NET\Framework\v2.0.50727\InstallUtil.exe "C:\MyService\MyService.exe"

Instead of

C:\WINDOWS\Microsoft.NET\Framework\v4.0.30319\InstallUtil.exe "C:\MyService\MyService.exe"

Solution 4:

Since only one version of the run-time can be loaded into a process (although, as others have alluded, backwards loading - 4.0 loading 2.0 - is okay), you have a few options:

Upgrade the .Net 2.0 project
Wrap the .Net 2.0 project (if the source is not yours)
Downgrade the .Net 4.0 project
Load the .Net 4.0 project into it's own process (I believe this can work - but will take a bit of effort, IMO)

Solution 5:

You'll either have to upgrade the .NET 2 project to .NET 4, or downgrade the .NET 4 project to .NET 3.5 (or earlier).

How do you upgrade the .net version? I am not sure where to and what to specify. Please help.

Edit: I found the answer myself. Select the project, right click and choose Property Pages. There you can select framework version. or select the project and click Shift+F4