Module fails dependency check in python script

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When I attempt to install a module I just built into ROS, it fails to 'find' a required package because of an error in the associated check_deps.py file. The dependency it is trying to find is package genmsg, which is in fact installed (I even reinstalled, just in case). The Python file genmsg_check_deps.py is producing a Python error very early, during start-up, at the line: from genmsg import EXT_MSG, EXT_SRV, MsgContext claiming that there is no module named genmsg.

But of course this Python file itself is in lib/genmsg

We are using ROS Jade