Issue
When attempting to open a Nintex Task Form, the following error appears:
System.ArgumentNullException: Value cannot be null. Parameter name: formKey
at Nintex.Workflow.Forms.ControlTemplates.TaskForm.GetForm(String formKey, FormData formData, Boolean hasEnterpriseLicense)
at Nintex.Workflow.Forms.ControlTemplates.TaskForm.ConfigureFiller(Boolean hasEnterpriseLicense)
at Nintex.Workflow.Forms.ControlTemplates.TaskForm.InitialiseForm(Boolean hasEnterpriseLicense)
at Nintex.Workflow.Forms.ControlTemplates.TaskForm.OnInit(EventArgs e)
at System.Web.UI.Control.InitRecursive(Control namingContainer)
at System.Web.UI.Control.InitRecursive(Control namingContainer)
at System.Web.UI.Control.AddedControl(Control control, Int32 index)
at Microsoft.SharePoint.WebPartPages.ListFormWebPart.CreateChildControls()
at System.Web.UI.Control.EnsureChildControls()
at Microsoft.SharePoint.WebPartPages.WebPart.get_WebPartMenu()
at Microsoft.SharePoint.WebPartPages.ListFormWebPart.CreateWebPartMenu()
at Microsoft.SharePoint.WebPartPages.WebPart.OnWebPartMenuCreate(Object sender, EventArgs s)
at System.Web.UI.Control.OnLoad(EventArgs e)
at Microsoft.SharePoint.WebPartPages.ListFormWebPart.OnLoad(EventArgs e)
at System.Web.UI.Control.LoadRecursive()
...
at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)
System.ArgumentNullException: Value cannot be null. Parameter name: formKey
at Nintex.Workflow.Forms.ControlTemplates.TaskForm.GetForm(String formKey, FormData formData, Boolean hasEnterpriseLicense)
at Nintex.Workflow.Forms.ControlTemplates.TaskForm.ConfigureFiller(Boolean hasEnterpriseLicense)
at Nintex.Workflow.Forms.ControlTemplates.TaskForm.InitialiseForm(Boolean hasEnterpriseLicense)
at Nintex.Workflow.Forms.ControlTemplates.TaskForm.OnInit(EventArgs e)
at System.Web.UI.Control.InitRecursive(Control namingContainer)
at System.Web.UI.Control.InitRecursive(Control namingContainer)
at System.Web.UI.Control.AddedControl(Control control, Int32 index)
at Microsoft.SharePoint.WebPartPages.ListFormWebPart.CreateChildControls()
at System.Web.UI.Control.EnsureChildControls()
at Microsoft.SharePoint.WebPartPages.WebPart.get_WebPartMenu()
at Microsoft.SharePoint.WebPartPages.ListFormWebPart.CreateWebPartMenu()
at Microsoft.SharePoint.WebPartPages.WebPart.OnWebPartMenuCreate(Object sender, EventArgs s)
at System.Web.UI.Control.OnLoad(EventArgs e)
at Microsoft.SharePoint.WebPartPages.ListFormWebPart.OnLoad(EventArgs e)
at System.Web.UI.Control.LoadRecursive()
...
at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)
Resolution
Please ensure that the Nintex task form is generated from within the Nintex Workflow task action itself, rather than from the Nintex Workflow content type on the Task list.