I resolve this error by copying two files like
(1)EntityFrameworkCatalog.xml file
(2)EntityFrameworkConfig_6_0_0.xsd
from
https://entityframework.codeplex.com/SourceControl/latest#src/EFTools/setup/EFToolsMsi/XmlSchemas/EntityFrameworkCatalog.xml
and place those files in "C:\Program Files\Microsoft Visual Studio 10.0\Xml\Schemas" folder.
At first download the entire zip file from above link.
From that extract the above two files(xml,xsd) from the below location
"src\EFTools\setup\EFToolsMsi\XmlSchemas". and copy to "C:\Program Files\Microsoft Visual Studio 10.0\Xml\Schemas" .
Why because day by day software is updated.Because of that reason we have to work with updated softwares.
(or)
You can install the EF6 Designer for VS2012 from
"
http://www.microsoft.com/en-us/download/details.aspx?id=40762"
and it will update the schema that validates config files.
Note: While doing this you have to close visual studio.After completing all process,You have to restart Visual Studio.