Business Portal 6.0: "Microsoft.BusinessFramework.Security.AuthenticationException: Invalid user"

Issue:
Once you successfully installed and configured the basic setup of Business Portals 6.0 and few of them getting the following error due to wrong data on MBF (Microsoft Business Framework).
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Microsoft.BusinessFramework.Security.AuthenticationException: Invalid user.
at Microsoft.BusinessFramework.UserManager.VerifyUser()
at Microsoft.BusinessFramework.EnterpriseSession.Initialize(String enterpriseUrl)
at Microsoft.BusinessFramework.Security.EnterpriseInitializationModule.OnAcquireRequestState(Object sender, EventArgs e)
at System.Web.HttpApplication.SyncEventExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute()
at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously)
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Solution: 
While adding the user in MBF you must notice and add it, for example if you are going to add the user "testuser1" and the domain name as "contoso.local",  the user must look like "contoso\testuser1" but nor "contoso.local\testuser1" because both are not same.

Reference: https://community.dynamics.com/gp/f/32/p/120598/252918.aspx#252918