ISSUE
After upgrade into Nintex Workflow 2013 version 3.2.4.20, user unable to access the Workflow Inventory page. ERROR CODE
From ULS Logs nintexworkflow_workflowgallery_aspx.ProcessRequest(HttpContext context) at System.Web.HttpApplication.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously)RESOLUTION
This is a known issue and the hot fix version 3.2.4.22 has been released.