In IEEE conferences is it necessary run the simulation in front of the members? My paper was accepted to an IEEE conference, but I am not getting the simulation results I obtained before.

In IEEE conferences will they tell you to run the simulation in front of them?
Since the other answers should properly address your question, I'll raise an issue that bothered me from the go: What do you mean you can't replicate your results?

One of the cornerstones of science is the replication of results (something that is almost never done in computer science...). If you can't replicate your results, how do you expect someone else to? If nobody can replicate/verify your results, sorry, you are not doing science :(

I'm not saying that you are doing it wrong, one would need more information than that, I'm saying that the phrase 


  but I am not getting the simulation results I obtained before.


is very troubling and can indicate that you are, indeed, doing something wrong.