Getting “type or namespace name could not be found” but everything seems ok?

Question

I\'m getting a:

type or namespace name could not be found

error for a C# WPF app in VS2010. This area of code was compiling fine

Answer 1

It event happen in Visual Studio 2017.

1. Restart Visual Studio
2. Clean project that fail to build.
3. Rebuild the project.

Answer 2

This can be the result of a .Net framework version incompatibility between two projects.

It can happen in two ways:

1. a client profile project referencing a full framework project; or
2. an older framework version targeting a newer framework version

For example it will happen when an application is set to target the .Net 4 Client Profile framework, and the project it references targets the full .Net 4 framework.

So to make that clearer:

• Project A targets the Client Profile framework
• Project A references Project B
• Project B targets the full framework

The solution in this case is to either upgrade the framework target of the application (Project A), or downgrade the target of referenced assembly (Project B). It is okay for a full framework app to reference/consume a client profile framework assembly, but not the other way round (client profile cannot reference full framework targeted assembly).

Note that you can also get this error when you create a new project in VS2012 or VS2013 (which uses .Net 4.5 as the default framework) and:

• the referencing project(s) use .Net 4.0 (this is common when you have migrated from VS2010 to VS2012 or VS2013 and you then add a new project)

• the referenced projects use a greater version i.e. 4.5.1 or 4.5.3 (you've re-targeted your existing projects to the latest version, but VS still creates new projects targeting v4.5, and you then reference those older projects from the new project)

Answer 3

I had the same issue. One night my project would compile the next morning ERRORS!.

I eventually found out that visual studio decided to "tweak" some of my references and point them elsewhere. for example:

System.ComponentModel.ISupportInitialize somehow became "blahblah.System.ComponentModel.ISupportInitialize"

Quite a rude thing for vs to do if you as me

Answer 4

A trickier situation I ran into was: Project one targets the 4.0 full framework with Microsoft.Bcl.Async package installed. Project two target the 4.0 full framework but would not compile when reference a Project one class.

Once I installed the Async NuGet package on the second project it compiled fine.

Answer 5

Ok, years later using VS 2017 .NET Core 2.2 Razor Pages I feel this answer might help someone. If it was a snake it would have bit me. I was throwing stuff around, changing names, renaming Models, and all of a sudden I got this error:

Error CS0246 The type or namespace name 'UploadFileModel' could not be found (are you missing a using directive or an assembly reference?)

This was underlined in red in my .chstml Razor Page. (not underlined after fix):

@page
@model UploadFileModel

So, finally, and luckily, I found the code from someone else that I had originally used, and low and behold, the namespace did not include the .cshtml file name!!!

Here is my bad dummy error spank myself with the page name in the namespace:

namespace OESAC.Pages.UploadFile
{
    public class UploadFileModel : PageModel
    {

What my original code had and all I had to do was delete the page name from the namespace, UploadFile:

namespace OESAC.Pages
{
    public class UploadFileModel : PageModel
    {

And low and behold, all the errors disappeared!! Silly me. But you know, MS has made this .NET C# MVC stuff really confusing for us non-computer scientists. I am constantly tripping on my shoelaces trying to figure out model names, page names, and syntax to use them. It shouldn't be this hard. Oh well. I hope error and solution helps someone. The error was right, there is no Namespace named "UploadFileModel" haha.

Answer 6

Reinstalling nuget packages did the trick for me. After I changed .NET Framework versions to be in sync for all projects, some of the nuget packages (especially Entity Framework) were still installed for previous versions. This command in Packages Manager Console reinstalls packages for the whole solution:

Update-Package –reinstall