After upgrading to Forms Version 2.11.5.20 the below error is produced when accessing the task.



In the ULS logs you’ll find the below error:
Failed to handle from host page on initialize event. Error: Outcome information is not available



See the below stack trace:
Failed to handle form host page on initialize event. Error: Outcome information is not available.. Stack trace:  
 at Nintex.Workflow.HumanApproval.Approver.LoadAvailableOutcomes()   
 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)


 

Install the hotfix released to resolve this issue:
https://files.nintex.com/link/7Mv3AZagFAPkeEd3Gm9eJa

If the above link does not work, please install the latest build of Nintex Forms for SharePoint 2013.