NameError: name 'dx' is not defined persists on Ubuntu 16.04 LTS


I have been using Netgen/NGSolve on 64-bit Ubuntu 16.04 LTS for the past 6 months. I installed it using Conda.
Only recently have I encountered the following error
NameError: name ‘dx’ is not defined
with codes involving dx.
I followed the advice on:
Can not run example
(Can not run example - Kunena)
but in vain.
More info:

packages in environment at /home/nssharma/anaconda2/envs/ngsolve_test:

netgen 6.2.2006 py37he358ceb_3 conda-forge
ngsolve 6.2.2006.post48 py37_0 ngsolve

Can you please help me fix this?

Many thanks,

Ubuntu 16.04 is end of life and does not provide updates for packages any more. And because of this you have an old version 2006 of ngsolve. You either have to build from source or update your distro.
Best Christopher