An item with the same key has already been added

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EnvironmentProduct: Sitefinity
Version: 5.x, 6.x, 7.x, 8.x, 9.x, 10.x
OS: All supported OS versions
Database: All supported Microsoft SQL Server versions
Question/Problem Description
An item with the same key has already been added error appears when submitting a form.

Server Error in '/' Application. 

An item with the same key has already been added. 

Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code. 

Exception Details: System.ArgumentException: An item with the same key has already been added. 

Source Error: 
An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below. 

Stack Trace: 
[ArgumentException: An item with the same key has already been added.] 
System.ThrowHelper.ThrowArgumentException(ExceptionResource resource) +56 
System.Collections.Generic.Dictionary`2.Insert(TKey key, TValue value, Boolean add) +13737545 
Telerik.Sitefinity.Modules.Forms.Web.FormsHelper.GetFormPostedData(IEnumerable`1 controls) +1177 
Telerik.Sitefinity.Modules.Forms.Web.UI.FormsControl.CreateFormValidatingEvent(IFormEntryResponseEditContext formEntryResponseEditContext, IList`1 controlsSate) +33 
Telerik.Sitefinity.Modules.Forms.Web.UI.FormsControl.ProcessFormSaving() +305 
System.Web.UI.WebControls.Button.OnClick(EventArgs e) +11762653 
System.Web.UI.WebControls.Button.RaisePostBackEvent(String eventArgument) +150 
System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +6016
Steps to Reproduce
Clarifying Information
Error MessageAn item with the same key has already been added.
Defect/Enhancement Number
Two of the input fields have identical FieldName for their meta field property.
1. Check each field for their meta field FieldName.
    - for Web Forms: Edit > Advanced > MetaField > FieldName
    - for MVC: Edit > Advanced > Model > MetaField > FieldName
2. Once the input fields with identical FieldName are identified remove one of them and replace it with new one.
3. Save changes

Note: By removing an input field, all previous data for that field will be removed from the database.
Last Modified Date6/19/2017 6:33 AM

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