Dynamics CRM Import Solution Failure

Failure Error:- An item with the same key has already been added.

Because of "duplicate field names", there are 2 possible causes.
1)Duplication has occurred between a custom field, and a virtual field

CRM creates an additional attribute in the metadata for the text of the field for certain field types (boolean, picklist and lookup). This attrbiute is not physically stored, and is considered to be a 'virtual' field. The virtaul attribute has the name of the base field + a suffix of 'name'.
For example,
the addresstypecode picklist field  => addresstypecodename virtual field
new_parentcustomerid custom lookup field  => new_parentcustomeridname virtual field.

CRM will let you do this, but the import could fail.

The following script will list of any duplicates, run in the METABASE database

select
    e.name as entity, a.name as attribute, count(*)
from
    attribute a join entity e on a.entityid = e.entityid
group by
    e.name, a.name
having count(*) > 1

MS Dynamics CRM Solutions

CRM Customizations - Customize through a web-based interface without any programming expertise or use the MS Dynamics CRM software development kit (SDK) to programmatically alter the metadata. Two default security roles associated with system customization privileges: System Administrator and System Customizer

Solutions are packages of customizations and metadata that allow system administrators and software developers to create, transport, and maintain business applications or functionality that run on the Microsoft Dynamics CRM framework.

Settings area -> Click Customizations ->  Click Customize the System to open the solution.

Microsoft Dynamics CRM 2011 Data Management - Import, Export, Duplicate & Delete

Import

• CRM Import Files formats: XML Spreadsheet 2003 (.xml), Comma-separated values (.csv), Rext (.txt), Compressed files (.zip)
• Include a column for each required field on the entity into which you are importing the data.
• One import file for each type of entity. 
• Import multiple files into a single .zip file.
• Maximum 8 megabytes (MB) size for each import file. 
• Import Data Wizard basic process: Prepare the import files, Import the file and map the records & View the results and correct failures.
• Dynamics CRM allows you to create templates for your import that you can download from the system.  In the Settings area -> click Data Management - > click Templates for Data Import. OR On the application ribbon -> click the Import Data button -> select Download Template for Import.
• An import template outputs an XML file with all of the columns for the entity you selected:
• All possible data fields for the entity are included.
• All of the column headers are named and labeled correctly. 
• Required data field names are bold in the top row.
• Each cell provides additional information about the data that should go in the field, such as its  data type, maximum and minimum values, or maximum length.
• For option sets, the template displays a list of the possible values for the field. 
• If you try to enter a value that is not included in the option set or not in the format, you receive an error message
• On the application ribbon -> click the Import Data button OR click the File tab -> select Import  OR Data from the Tools menu -> The Import Data Wizard opens.