error export Nintex workflow

Issue 

When trying to export the Nintex workflow we got the following errors.

 Error #1

Server Error in '/' Application.

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Validation of viewstate MAC failed. If this application is hosted by a Web Farm or cluster, ensure that <machineKey> configuration specifies the same validationKey and validation algorithm. AutoGenerate cannot be used in a cluster.

http://go.microsoft.com/fwlink/?LinkID=314055

 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.Web.HttpException: Validation of viewstate MAC failed. If this application is hosted by a Web Farm or cluster, ensure that <machineKey> configuration specifies the same validationKey and validation algorithm. AutoGenerate cannot be used in a cluster.

http://go.microsoft.com/fwlink/?LinkID=314055

Error #2

Server Error in '/' Application.

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Cannot find workflow in repository.

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: Nintex.Workflow.NWException: Cannot find workflow in repository.

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:

[NWException: Cannot find workflow in repository.] Nintex.Workflow.WorkflowRepository.get_Item(Guid wfId) +673 Nintex.Workflow.ApplicationPages.ExportWorkflow.Page_Load(Object sender, EventArgs e) +990 [NWException: Error exporting workflow.] Nintex.Workflow.ApplicationPages.ExportWorkflow.Page_Load(Object sender, EventArgs e) +1523 Microsoft.SharePoint.WebControls.UnsecuredLayoutsPageBase.OnLoad(EventArgs e) +300 Microsoft.SharePoint.WebControls.LayoutsPageBase.OnLoad(EventArgs e) +49 System.Web.UI.Control.LoadRecursive() +71 System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +3178

This is happening because you are accessing the workflow from site setting-> Workflows gallery (Nintex Workflow section) in top the level site (root of the site collection).

You need to access the workflow from site Nintex menu.

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