SummaryWhen changing Single Line Text control "Connected to' field the error occurs. Failed to retrieve form control for canvas. Error: Object reference not set to an instance of an object.. Stack trace: at Nintex.Forms.SharePoint.Services.NfWcfService.GetUpdatedFormControlForCanvas(FormControlProperties formControlProperties, FormVariable variable).
SolutionMake sure a site collection is created at the root level for the web application where the error occurs. Please refer to the below article.