hah, what a laugh.
The solution was simply embarrassing.
Instead of what the program sugests as the router-ip, I had to add an accesport after that. And all went smoothly afterwards:
Router: ZyXEL - P-2602HW-D1A (ZyXEL Firmware)
Loading Commands...
Number Of Port Forwards To Send To Router (1)
Running Commands...
(Current - 1/1)
Adding test (TCP/UDP) For Ports 6113-6113 To 10.0.0.245()
Running Script From Database For Selected Router
-----------------------------------------------------------------------
Step 01. nav_first_only("")
(Successful) (
http://:chaGidoqui@10.0.0.1:2033/)
Step 02. set_password("LoginPassword")
(Successful)
Step 03. click_button_first_only("Login")
(Successful)
Step 04. set_frame_name("main")
Step 05. set_frame_number("3")
Step 06. nav("PortForwarding.html")
(Successful) (
http://:chaGidoqui@10.0.0.1:2033/PortForwarding.html)
Step 07. timeout("2000")
(Successful)
Step 08. check_if_name_exists("")
Step 09. timeout("2000")
(Successful)
Step 10. set_combobox_custom("PortFor_ServiceAdd,0,User define")
(Successful)
Step 11. timeout("5000")
(Successful)
Step 12. set_checkbox("PortRule_Active,0")
(Successful)
Step 13. set_name("PortRule_Name,0")
(Successful)
Step 14. set_start_port("PortRule_SPortStart,0")
(Failed - Object Not Found)
Step 15. set_stop_port("PortRule_SPortEnd,0")
(Failed - Object Not Found)
Step 16. set_start_port("PortRule_SPort,0")
(Successful)
Step 17. set_stop_port("PortRule_EPort,0")
(Successful)
Step 18. set_ip("PortRule_SrvAddr,0")
(Successful)
Step 19. set_start_port("PortRule_PortTrans_SPort,0")
(Failed - Object Not Found)
Step 20. set_stop_port("PortRule_PortTrans_EPort,0")
(Failed - Object Not Found)
Step 21. set_start_port("PortRule_DPortStart,0")
(Failed - Object Not Found)
Step 22. set_stop_port("PortRule_DPortEnd,0")
(Failed - Object Not Found)
Step 23. click_button("sysSubmit")
(Successful)
-----------------------------------------------------------------------
Finished Adding test
Sorry for wasting your time

I have one final question regarding my other pc:
when i installed the SPF and opened the program, it stuck on "loading routers". I've seen that someone else had the same issue, but can't see what you did to solve it.
- Thank you, Trends.