The Offline or Online Simulator relies on an external process to run correctly, com_e30.exe. If this process is running before the Simulator begins, it can interfere with how the Simulator works, causing the Port 8000 error. On your PC open Windows Task Manager » Processes tab. Check if com_e30.exe exists. If it does, end it and then run simulation again.
If the Port 8000 error is being caused by another software using port 8000, you can change the port used by the Simulator in EasyBuilder System Parameter Settings » Model tab.