You have declared a property containing a default clause, but the type property type is incompatible with default values.

  program Produce;

    type
      VisualGauge = class
        pos : Single;
  property Position : Single read pos write pos default 0.0;
      end;

  begin
  end.

The program above creates a property and attempts to assign a default value to it, but since the type of the property does not allow default values, an error is output.

  program Produce;

    type
      VisualGauge = class
        pos : Integer;
  property Position : Integer read pos write pos default 0;
      end;

  begin
  end.

When this error is encountered, there are two easy solutions: the first is to remove the default value definition, and the second is to change the type of the property to one which allows a default value. Your program, however, may not be as simple to fix; consider when you have a set property which is too large - it is this case which will require you to carefully examine your program to determine the best solution to this problem.