nuget 'packages' element is not declared warning

Actually the correct answer to this is to just add the schema to your document, like so

<packages xmlns="http://schemas.microsoft.com/packaging/2010/07/nuspec.xsd">

...and you're done :)

If the XSD is not already cached and unavailable, you can add it as follows from the NuGet console

Install-Package NuGet.Manifest.Schema -Version 2.0.0

Once this is done, as noted in a comment below, you may want to move it from your current folder to the official schema folder that is found in

%VisualStudioPath%\Xml\Schemas

You will see it only when the file is open. When you'll close the file in Visual Studio the warnings goes away

http://nuget.codeplex.com/discussions/261638

You can always make simple xsd schema for 'packages.config' to get rid of this warning. To do this, create file named "packages.xsd":

<?xml version="1.0" encoding="utf-8" ?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" elementFormDefault="qualified"
      targetNamespace="urn:packages" xmlns="urn:packages">
  <xs:element name="packages">
    <xs:complexType>
      <xs:sequence>
        <xs:element name="package" maxOccurs="unbounded">
          <xs:complexType>
            <xs:attribute name="id" type="xs:string" use="required" />
            <xs:attribute name="version" type="xs:string" use="required" />
            <xs:attribute name="targetFramework" type="xs:string" use="optional" />
            <xs:attribute name="allowedVersions" type="xs:string" use="optional" />
          </xs:complexType>
        </xs:element>
      </xs:sequence>
    </xs:complexType>
  </xs:element>
</xs:schema>

Location of this file (two options)

• In the same folder as 'packages.config' file,
• If you want to share packages.xsd across multiple projects, move it to the Visual Studio Schemas folder (the path may slightly differ, it's D:\Program Files (x86)\Microsoft Visual Studio 10.0\Xml\Schemas for me).

Then, edit <packages> tag in packages.config file (add xmlns attribute):

<packages xmlns="urn:packages">

Now the warning should disappear (even if packages.config file is open in Visual Studio).