reference and class namespace

I am having trouble linking to a secondary class in my project - I have attached 2 images which describe the problem best..

Pleas any a开发者_StackOverflow中文版dvice - I thank you in advance.

This error was two things - thank you everybody for your help. 1) add namespace to DB file

namespace C_Classes

{ using System; ...

public class DB

2) Change Target Framework in the Project Properties and change it to ".Net Framework 4" from "...Client Profile"

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I'm assuming you've added a Project reference to the C_Classes project?

Otherwise I've seen these types of issues when the project is set to target ".Net Framework 4 Client Profile" (which it sometimes sets as the default).

Check your Target Framework in the Project Properties and change it to ".Net Framework 4".

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Your snippet of (presumably) DB.cs doesn't show a namespace declaration - so the DB class is just in the global namespace. If you want it in the C_Classes namespace you'll need:

namespace C_Classes
{
    public class DB
    {
        // etc
    }
}

Unlike VB, a C# class doesn't end up in a namespace without a namespace declaration appearing in the source code.

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I couldn't see a namespace enclosing your DB class.

Enclose your DB class as shown below:

namespace C_Classes
{
    using System;
    ...

    public class DB
    {

    }
}

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Does the second project have a reference to the first one? That isn't made clear in the images provided. Expand the "References" folder in the second project and see if there's a reference to the first project there. If there isn't, just right-click on the "References" folder and add a Project Reference to it.

The second thing I notice is that there's no explicit namespace in the DB file. I'm not 100% sure if there's an implicit one when it's compiled in an assembly, but I wouldn't count on it. Try wrapping that class in an explicit C_Classes namespace and see if that helps.