www.neuron.yale.edu

I was examining the electrotonic properties of a model cell with the
Impedance Path tool. My custom GUI consisted of a CellBuilder,
a RunControl panel, and the Impedance Path tool. I saved this to
a ses file using File / save session, then exited NEURON. Later
I restarted NEURON and tried to recover the ses file but only the
CellBuilder and RunControl appeared--there was no Impedance Path
tool. However, the interpreter reported
/usr/local/nrn/i686/bin/nrniv: map : object prefix is NULL in bsz.ses near line 168
Did I do something wrong? Is there a workaround?

Using Version 5.7 2005-4-21 11:7:7 Main (159)

I see that none of the Impedance tools have the ability to save themselves into a session file. And none of them use the proper idiom for properly opting out of the session file, i.e. when the box holding the gui for the object is created one should use VBox.save("") where the argument is an empty string.

To work around the problem of an invalid session file that was supposed to contain the path impedance tool, edit the session file and remove the lines
//Begin Impx[0]
....
//End Impx[0]

To prevent such an invalid file from being constructed edit the file nrn/lib/hoc/impedanx.hoc and change
the line:
b1.save("save()")
to
b1.save("")