The version I'm running is 1.5.0 RC1, and earliy I used 1.4.5. I have tried this in more than three computers running WindowsXP, and got the same error as I described above, which is realy  a blow to the enthusiasm of learning Modelica for me.
I have tried 1.5.0 RC2 . It works good indeed.
Thanks a lot !

little body comes here

I am studying "Principles of Object-Oriented Modeling and Simulation with Modelica 2.1 (Peter Fritzson )". An example is as follows:
class Pendulum  "Planar Pendulum"
  constant  Real PI=3.141592653589793;
  parameter Real m=1, g=9.81, L=0.5;
  Real F;
  output    Real x(start=0.5),y(start=0);
  output    Real vx,vy;
equation
  m*der(vx)=-(x/L)*F;
  m*der(vy)=-(y/L)*F-m*g;
  der(x)=vx;
  der(y)=vy;
  x^2+y^2=L^2;
end Pendulum;

when:
simulate(Pendulum, stopTime=4)
plot(x)
it shows a figure the same as the book.


But when stopTime=5 or other value, the result seems to be completely wrong.


Can anybody tell me why?