Hello,
Shutting down the firewalls on both PCs is not enough.
Other security settings inside windows regarding DCOM must be adapted.
Look at this entry http://support.automation.siemens.com/WW/view/en/22033262

There is also an icon "configuration Console" on your desktop when Simatc Net is installed.

You will find a "security" point in that console.

With a single buuton click you can apply required settings also.