Connect Float output to Float input causes an error I am playing around with animation nodes, so I have a bunch of instances along a spline. As you see in the working node tree, instances 31.00 and a Math node socket B also set as 31.00. 

So now you think, OK I'll drive the math value by the number of instances, which would be the same float number. Wrong! If you do this everything goes RED and the whole world is destroyed!!!

Why can I not connect these two nodes?
As pointed out by Jacques, in the problems panel we can see what has caused this issue. I highlighted this in red.



What I needed to do was to use another socket on the subprogram and loop input nodes, I have also highlighted these in red on the node tree.



Finally here is what the node tree produces, nothing spectacular but at least I'm learning how to use the amazing Animation Nodes addon.