Question
We have a Norway Maple and last spring we attached a zip line to it which included tapping a few nails into it and this winter we found it dripping a sticky substance and wonder if it is bad and if it is caused by the zip line.

Answer
Yes the attachment of the zip line caused the sap. It would be the same as tapping into a maple to get maple sap for syrup as is done in the Eastern US. The "nails" broke the seal of the bark and allowed the trees sap to ooze out. It will stop over time as the wound calluses over but in time you can expect decay fungi to enter the wound and the nails will pull out from the decaying wood. Never a good idea to nail into a tree. It will not kill the tree but may cause a hollow area to start where the nails are.