Visual Studio 2010 -- are you missing a using directive or an assembly reference?

When I add a reference to my dll in Visual Studio project, I am able to use it, but when I compile my code or try to run it, I get an are开发者_开发问答 you missing a using directive or an assembly reference?_ Error. I am able to confirm that I have the right using statement for my namespace and I am able to confirm that the dll is correctly loaded. Anyone have any idea what I may not have right in this?

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Go to project settings and make sure that you are not compiling the project for a .net version that includes the text "client profile".

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I had just had an issue precisely like this, even if this is an old question thought I would add my 2c on what fixed it as none of the other answers helped:

For whatever reason, when I built the solution top to bottom a certain dll was not getting updated and output that held changed code. So while my solution had no visible errors, when you attempted to build, it was still referencing the old dll and started complaining.

It was simply a case of directly re-building the offending project and after that it picked up the latest dll and built happily.

This seemed to be a freak accident as no configuration had changed between when it worked / when it didn't.

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Sometimes, JUST REBUILD THE SOLUTION.

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The location of the DLL is important.

If you add a reference on your local machine to a DLL that is outside of your Visual Studio solution, it isn't necessarily copied into your solution files (depends on the type of solution/project).

If this is your problem, then you need to either put the DLL in the same path on the other machine, or copy it into your solution so it gets deployed along with the solution files, and change the reference.

You can also handle this with build instructions, but that might be beyond your aspirations at the moment.

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Most likely your dll is referencing another dll that the client project is not referencing and your dll code is exposing a type or an interface from the 3rd dll to the client code.

If you post the exaCt message, we'll be able to help better.

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Are you using .net 4.0?

If yes, this dll is probably not compatible with .net 4.0

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In my case, the main project (WinForm) was configured Framework Target: FW 4.0 "client profile". I change to FW 4.0 and work perfect!!. At first time i was looking in the referenced projects and they were ok, but de main project doesn't. I hope this help. Thank you.

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In my case this compilation error has gone after adding the reference to Microsoft BCL Build Components via "Manage NuGet packages" context menu on problem project.

Before: I had project Main (console application) referencing project A (class library). Project A had dependency on Microsoft BCL Build Components.

After: I started refactoring where I picked out several classes to the separate project New. It also depended on A. But the compilation error occurred on project New as if there was no reference New -> A (although Visual Studio didn't highlight allegedly not found interfaces and classes listed in the error list of compilation).

So I checked project A's dependencies and found there Microsoft BCL Build Components. After adding it to New's dependencies everything worked fine. The most interesting thing is that Main did not contain this dependency and it didn't need it.

Hope this helps.

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You just Have to check your namespace of that class file again...it will work