TimeBill record

I am trying to insert new TimeBill record against SupportIssue. I end up with an error: "Invalid casetaskevent reference key"... What am I doing wrong ?

 RecordRef issue     = new RecordRef();  issue.type          = RecordType.supportCaseIssue;  issue.typeSpecified = true;  issue.internalId    = Console.ReadLine();      // create random hours   Random rnd   = new Random();  string hours = "";  int r        = rnd.Next();  hours        = (r % 24).ToString() + ":";  hours        = hours + (r % 60).ToString();    // create new employee record based on logged in user  RecordRef emp     = new RecordRef();  emp.internalId    = service.sessionInfo.userId;  emp.type          = RecordType.employee;  emp.typeSpecified = true;    // creat new TimeBill record  TimeBill bill      = new TimeBill();  bill.caseTaskEvent = issue;  bill.createdDate   = DateTime.Now;  bill.tranDate      = DateTime.Now;  bill.employee      = emp;  bill.memo          = "My comment #" + r.ToString();  bill.hours         = hours;  bill.isBillable    = false;    // will fail with an error "Invalid casetaskevent reference key"...   // I know