When using the Telerik upgrade wizard I get a error while upgrading my web app:

 

An error occurred while running the wizard.

Error executing custom action Telerik.KendoUI.Mvc.VSX.Actions.MultiProjectUpdateReferencesAction: System.NullReferenceException: Object reference not set to an instance of an object.
   at Telerik.VSX.Internal.ProjectManagement.ProjectAssemblyReferenceBase.Equals(AssemblyWrap assemblyReference)
   at Telerik.VSX.ProjectConfiguration.ProjectReferenceManager.EnsureDifferentExistingReferenceRemoved(AssemblyWrap assemblyReference)
   at Telerik.VSX.ProjectConfiguration.ProjectReferenceManager.AddAssemblyReference(AssemblyWrap assemblyReference)
   at Telerik.VSX.ProjectConfigurators.ApplicationReferenceManager.AddReferences()
   at Telerik.VSX.ProjectConfigurators.ApplicationReferenceManager.UpdateReferences()
   at Telerik.VSX.Actions.UpdateReferencesAction.UpdateReferences(IProjectWrapUIComponents projectWrap)
   at Telerik.VSX.Actions.UpdateReferencesAction.Execute(WizardContext wizardContext, IPropertyDataDictionary arguments, IProjectWrap project)
   at Telerik.VSX.Actions.ProjectActionBase.Telerik.VSX.Actions.IProjectAction.Execute(IWizardContext wizardContext, IPropertyDataDictionary arguments, IProjectWrap projectWrap)
   at Telerik.VSX.Actions.MultiProjectActionBase`1.Execute(WizardContext wizardContext, IPropertyDataDictionary arguments)
   at Telerik.VSX.Actions.MultiProjectUpdateReferencesActionBase`1.Execute(WizardContext wizardContext, IPropertyDataDictionary arguments)
   at Telerik.VSX.WizardEngine.Actions.ActionBase.Telerik.WizardFramework.IAction.Execute(IWizardContext wizardContext, IPropertyDataDictionary arguments)
   at Telerik.VSX.WizardEngine.ActionManager.ExecActions()