So … I did some testing with the ScopeIf node, but sadly it didn’t work for me, as needed.
I tried several things like placing it directly in my graph, putting it within a custom node and even node within node, but I always got the same two results:
Either It made my complete graph go null from the beginning, so the error detection already got null inputs and making the whole graph useless.(doesn’t make any sense at all)
Or the ScopeIf didn’t effect the other nodes within the graph. (No matter if true or false input reached the scopeif)
Maybe I´m not using it correctly. … Dunno 
So, to solve my problem, I decided to go for the flow control by a combination of Codeblocks and IF (Passthrough) nodes.
Suppressing the entire data stream through passthrough gates, directly after the error checks, made the graph stop within a few seconds, by the event of error. 
At last I have to say, … let’s see, maybe in the future there are better ways to control the flow of a graph or even stop it mid run. 