First off I want to thank Peter, Craig and you Steve for replying so fast.
I don't want to be a "wise guy" but, I read some examples of programs which I used to establish what I wrote.
Now in one example: T0_int.asm written by Peter a port pin is inverted every second.
I translated that into my address at 3FF0h, this should toggle a flip/flop at that location. This works, because I see the LED attached to it lighting up.
This is where my watchdog is connected to.
When I try to use the complete T0_int.asm file and compile it I get a sync error at org 000Bh.
Maybe in some time I will be able to find some logic but I'm still very lost.