@Balwyn Yes, you could try setting both the paths in full. I was forgetting that your .exe is probably not in the Pd/bin folder (I use it a lot with "wish.exe" while I am trying to build widgets to link to a tcl popup)......... so you could try putting the executable in the "bin" folder.....
I am in the same boat as you and @monetus.. I can get tcl/tk to do stuff, especially if I write a plugin for what I am trying to achieve. I can get popups to write back to the $::focused_window....... and so place objects into the window from which the popup was actioned...... but those objects have to be defined in the plugin. The next step is to write what I want into the objects, and automate their connection back to the call that activated the popup....... I am away working on shows for a while, so I might have time during the days to get a bit further.
What I want, and you and Monetus really need is is an object like [sys_gui] that can receive variables that are asked for.......... then widgets can be created that can send user input or user selected input back to Pd. I am nearly there.... but I would not object if someone else manages it first!
Have a look at this thread......... http://forum.pdpatchrepo.info/topic/10131/gui-plugins-where-are-redraw-colors-stored/7 where I posted more or less as far as I have travelled.....
David