function returns IsValid as false when both records exist

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Delphi

The aim of the code below is to find and open a loan record and a member record. Since I'm creating a library system where the user does not have a card with a barcode, they have to remember the Unique ID so i thought it would be easier if they only have to remember one number that is the Unique ID to all their relevant records. However the code below has an error in that the function returns IsValid as false when both records exist. Help?

procedure RecordCheck(var MemberID: integer);
var
  IsValid: boolean;
  { Procedure to check that Records exist }

  function ValidateID(Member_ID: integer): boolean;
  var
    Error: boolean; { True/False- false until there is an error }
    Count: integer; { For each letter and number }
 begin
    Error := false;
    AssignFile(MemberDetailsFile, 'MemberDetails.dat');
    Reset(MemberDetailsFile);
    while not eof(MemberDetailsFile) do
    begin
      read(MemberDetailsFile, MemberRecords);
      if  Member_ID = MemberRecords.UniqueId then
      begin
        { if match/record found }
        Error := false;
        end
        else
        Error := true
      end;
    begin
      AssignFile(LoanFile, 'LoanFile.dat');
      Reset(LoanFile);
      while not eof(LoanFile) do
      begin
        read(LoanFile, LoanRecords);
        if not Member_ID = LoanRecords.LoanUniqueId  then
        begin
          Error := true
        end
        else
          result := not Error;
      end; { of Check }
    end;
  end;

begin
  IsValid := ValidateID(MemberID);
  if IsValid = false then
    if MessageDlg('The Member ID or loan record does not exist! Try again?',
      mtConfirmation, [mbYes, mbNo], 0) <> mrYes then
    begin
      { if user chooses not to try again }
      frmLoanProductsIDConfirm.Close;
      frmIssue.Show;
      exit;
    end
    else
    begin
      { if user chooses to try again }
      frmLoanProductsIDConfirm.Show;
      frmIssue.Hide;
    end;
  if IsValid = true then
    frmIssueProd.Show;
    frmIssue.Close;
    frmLoanProductsIDConfirm.Close;
end;