Recruit >> Server error occurred on Preliminary questionnaire screen

on demo company DC, while candidate is applying to Job and logging in using linkedin credentials, Server error occurred on Preliminary questionnaire screen on save button.

PFA error log and screen shot.

Exception : The INSERT statement conflicted with the FOREIGN KEY constraint "FK_CandidateJobApplications_Candidate". The conflict occurred in database

"Burnham_11695", table "rct.Candidate", column `ID`.Cannot insert the value NULL into column `CandidateJobApplicationsID`, table

`Burnham_11695.rct.WorkFlowSummary`; column does not allow nulls. INSERT fails.The statement has been terminated.The statement has been terminated.
App Error Log : ControllerAppTier.Save->RecruitControllerAppTier.Save->Candidate.SaveQuestionniareAnwers
Employee ID : 0
Action Name : SaveQuestionniareAnwers
Model : System.Web.Mvc.HandleErrorInfo
Controller : PlatformSharedBase
Web Error Log : at WORKTERRA.Recruit.RecruitControllerWebTier.Save(ObjectType I_objectType, Hashtable I_criteria, Object I_context)
at WORKTERRA.Models.RecruitApplyJobModel.ApplyJob(String JobId, String CandidateID)
at WORKTERRA.Shared.Controllers.PlatformSharedBaseController.SaveQuestionniareAnwers(String JobId, String CandidateID)
at lambda_method(Closure , ControllerBase , Object[] )
at System.Web.Mvc.ReflectedActionDescriptor.Execute(ControllerContext controllerContext, IDictionary`2 parameters)
at System.Web.Mvc.ControllerActionInvoker.InvokeActionMethod(ControllerContext controllerContext, ActionDescriptor actionDescriptor, IDictionary`2

parameters)
at System.Web.Mvc.ControllerActionInvoker.<>c_DisplayClass13.b_10()
at System.Web.Mvc.ControllerActionInvoker.InvokeActionMethodFilter(IActionFilter filter, ActionExecutingContext preContext, Func`1 continuation)
at System.Web.Mvc.ControllerActionInvoker.InvokeActionMethodFilter(IActionFilter filter, ActionExecutingContext preContext, Func`1 continuation)
at System.Web.Mvc.ControllerActionInvoker.InvokeActionMethodWithFilters(ControllerContext controllerContext, IList`1 filters, ActionDescriptor

actionDescriptor, IDictionary`2 parameters)
at System.Web.Mvc.ControllerActionInvoker.InvokeAction(ControllerContext controllerContext, String actionName)