bad processing code: custom element

I have a click element called TagForwarder that takes 1 input and writes to
n output that is dependent on user configuration. So, to route packets
based on Layer7 contents that contain interesting tags tag1 and tag2, the
configuration would be:

tf::TagForwarder(tag1, tag2, -).
tf[0] -> packets containing tag1
tf[2] -> packets containing tag2
tf[3] -> Discard

Inside the code of the element:
1. The processing_code for the element returns the string "PUSH"
2.. port count function returns "1/-"

When I do the following:
Socket() -> tf::TagForwarder(tag1, tag2, -).;

tf[0] -> Socket()
tf[2] -> Socket()
tf[3] -> Discard


I get the warning message : "bad processing code"

Where's my mistake?