Please let us know your Inkscape version and check in the Inkscape extensions directories (the one in your user share/extensions directory and the one in your Inkscape installation share/extensions directory) if there are the following files:
hershey.py , hershey.inx and hersheydata.py
I am running Inkscape version 0.92 and yes, all of those extensions are there.
The error that comes up is with the Convert Text to Hershey extension, not with the Hershey text render function.
I am having two separate issues.
The render Hershey text function will only properly render one line of text in Makercam and the text to Hershey comes up with an error.
When I sent two merged lines of text to Makercam it looks something like this;
Two line text
S
e
c
o
n
d