#include "stdafx.h"
#include "Eigen\Core"
#include <iostream>
using namespace Eigen;
using namespace std;
typedef Eigen::Array<float, 6, 1 > Pixel2;
typedef Eigen::Array< Pixel2, 3, 1 > Pixel;
int main()
{
Eigen::Array< Eigen::Array<float, 6, 1 >, 2, 1 > data;
return 0;
}

1>------ Build started: Project: testtemplate, Configuration: Debug Win32 ------
1>Compiling...
1>testtemplate.cpp
1>c:\documents and settings\user\my documents\visual studio 2008\projects\testtemplate\testtemplate\eigen\src\core\densebase.h(366) : error C2039: 'dummy_precision' : is not a member of 'Eigen::NumTraits<T>'
1> with
1> [
1> T=Eigen::Array<float,6,1>
1> ]
1> c:\documents and settings\user\my documents\visual studio 2008\projects\testtemplate\testtemplate\eigen\src\core\arraybase.h(54) : see reference to class template instantiation 'Eigen::DenseBase<Derived>' being compiled
1> with
1> [
1> Derived=Eigen::Array<Eigen::Array<float,6,1>,2,1>
1> ]
1> c:\documents and settings\user\my documents\visual studio 2008\projects\testtemplate\testtemplate\eigen\src\core\plainobjectbase.h(66) : see reference to class template instantiation 'Eigen::ArrayBase<Derived>' being compiled
1> with
1> [
1> Derived=Eigen::Array<Eigen::Array<float,6,1>,2,1>
1> ]
1> c:\documents and settings\user\my documents\visual studio 2008\projects\testtemplate\testtemplate\eigen\src\core\array.h(57) : see reference to class template instantiation 'Eigen::PlainObjectBase<Derived>' being compiled
1> with
1> [
1> Derived=Eigen::Array<Eigen::Array<float,6,1>,2,1>
1> ]
1> c:\documents and settings\user\my documents\visual studio 2008\projects\testtemplate\testtemplate\testtemplate.cpp(20) : see reference to class template instantiation 'Eigen::Array<_Scalar,_Rows,_Cols>' being compiled
1> with
1> [
1> _Scalar=Eigen::Array<float,6,1>,
1> _Rows=2,
1> _Cols=1
1> ]
1>c:\documents and settings\user\my documents\visual studio 2008\projects\testtemplate\testtemplate\eigen\src\core\densebase.h(371) : error C2039: 'dummy_precision' : is not a member of 'Eigen::NumTraits<T>'
1> with
1> [
1> T=Eigen::Array<float,6,1>
1> ]
1>c:\documents and settings\user\my documents\visual studio 2008\projects\testtemplate\testtemplate\eigen\src\core\densebase.h(372) : error C2039: 'dummy_precision' : is not a member of 'Eigen::NumTraits<T>'
1> with
1> [
1> T=Eigen::Array<float,6,1>
1> ]
1>c:\documents and settings\user\my documents\visual studio 2008\projects\testtemplate\testtemplate\eigen\src\core\densebase.h(373) : error C2039: 'dummy_precision' : is not a member of 'Eigen::NumTraits<T>'
1> with
1> [
1> T=Eigen::Array<float,6,1>
1> ]
1>c:\documents and settings\user\my documents\visual studio 2008\projects\testtemplate\testtemplate\eigen\src\core\densebase.h(374) : error C2039: 'dummy_precision' : is not a member of 'Eigen::NumTraits<T>'
1> with
1> [
1> T=Eigen::Array<float,6,1>
1> ]
1>Build log was saved at "file://c:\Documents and Settings\User\My Documents\Visual Studio 2008\Projects\testtemplate\testtemplate\Debug\BuildLog.htm"
1>testtemplate - 5 error(s), 0 warning(s)
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========

You define arrays where each item is an array and somewhere in your code, you try to call methods which are defined only on scalars, like dummy_precision() (See the output from the compiler)