In the recent 2.0.0.M4 release, there have been two issues found with the simulation:
1) When performing SCA Java based simulation, the nodes on the purchasing example's SuccessfulPurchase.scn only show yellow and red nodes, instead of the expected all green nodes.
This may be due to a JRE issue. If you check the Error Log (Windows->Show Views->Others->Error Log) it will record an error if this is the case. If this happens, then you will need to go to the Window->Preferences->Java->JREs and configure (and use) a different JRE.
It would also be useful if you could let us know the platform and JRE versions that were found to not work (and the ones that did), so that we could compile a list.