The type or namespace name 'Linq' does not exist in the namespace 'System'

Question

When I want to use button to write code in C# it doesn't go to the ".cs" file to write C# code. When I check the project source, I found this error:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;

Severity Code Description Project File Line Error CS0234 The type or namespace name 'Linq' does not exist in the namespace 'System' (are you missing an assembly reference?) Golestani C:\Users\javad\Documents\Golestani\Login.aspx.cs 3

Solution 1

I had an issue with System.Linq not being recognized. The way I solved it was to change the targeted framework of my website from 4.0 to to 3.5 and then switch back to the original targeted framework (in my case 4.0)

1. Hit Shift+F4 or right click at the project level and select Property Pages in Visual Studio. (Alt+Enter or right click at the project level and select Properties in VS2017.)
2. Change the Target Framework from .Net Framework 4 to .Net Framework 3.5
3. Confirm with OK
4. Repeat this process in reverse so, again hit Shift+F4
5. Change it back from .Net Framework 3.5 to .Net Framework 4

Hope this helps

Solution 2

Try to Unload and then reload the concerned project. That will do it.

Solution 3

Put this piece of code in the Configuration file (Web.config) and test it.

<compilation debug="false">
<assemblies>
<add assembly="System.Core, Version=3.5.0.0, Culture=neutral, PublicKeyToken=B77A5C561934E089"/>
<add assembly="System.Xml.Linq, Version=3.5.0.0, Culture=neutral, PublicKeyToken=B77A5C561934E089"/>
<add assembly="System.Design, Version=2.0.0.0, Culture=neutral, PublicKeyToken=B03F5F7F11D50A3A"/>
<add assembly="System.Web.Extensions.Design, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35"/>
<add assembly="System.Windows.Forms, Version=2.0.0.0, Culture=neutral, PublicKeyToken=B77A5C561934E089"/>
</assemblies>
</compilation>

Solution 4

Visual Studio 2015 References -> Add Reference -> Assemblies -> select System.Data.Linq

Solution 5

Try this one. Maybe targetFramework="4.0" will work. Worked for me.

<compilation debug="false" targetFramework="4.0">
<assemblies>
<add assembly="System.Design, Version=4.0.0.0, Culture=neutral, PublicKeyToken=B03F5F7F11D50A3A"/>
<add assembly="System.Web.Extensions.Design, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35"/>
<add assembly="System.Windows.Forms, Version=4.0.0.0, Culture=neutral, PublicKeyToken=B77A5C561934E089"/>
</assemblies>
</compilation>

View more solutions

Comments

[javad]

What Do You Mean??

[Hamed]

Right click your project -> Add Reference -> select Framework tab -> select System.Core

[AmirHossein Rezaei]

Go to project -> References -> Add Reference -> -> Assemblies -> Search for "System.Xml.Linq" and check it.

[Malcolm Anderson]

If Shift+F4 doesn't work, just right click at the project level and select "Property Pages"

[EricImhauser]

That did work for me after hours of research. Thanks

[user2163234]

VS is nice when it works, but its some ungodly Frankenstein collection of stuff and things go to hell frequently and are a nightmare figure out. It's frustrating when you decide to reinstall windows just to get VS to work again. Teach me to try to use it for R and Python and still expect C# to work too.

[Aron Boyette]

I had success with this change, although I only needed to do System.Core. And for those who haven't memorized the the Web.config XML schema, the <compilation> element goes under <system.web>. @Hamed, I urge you to change your answer to include <system.web> and to fix the syntax highlighting.

[blind Skwirl]

yup, just closing and reopening VS2017 did it for me. Happens often for various issues.

[yu yang Jian]

This action may change the content of web.config, suggest to check what content is modify after change, to ensure that no function is thus disabled.

[Marco Aurelio Fernandez Reyes]

In my case (changing from Framework 2.0 to Framework 3.5) fixed the problem. Thank you.

[Rajesh Thampi]

Worked on Windows 2008 R2 for an age old intranet website. Thank you.

[wallef]

This worked for me in VS 2022