Error: Unable to read DOLFIN XML data

Hi everyone,
I am first using fenics in an attempt to simulate the evolution of a tumor. Hoping to have carried out all the installation steps of fenics (and dolfin) correctly, I am having problems trying to get the right .xml and .pvd files respectively for the execution of the diffusion simulation and for the visualization with paraview.
In particular, in particular from such commands (defDT.py is the code that should produce the indicated outputs) I get the following output:

(base) MAC-2:~ lorenzomarta$ conda deactivate

MAC-2:~ lorenzomarta$ conda activate fenicsproject

(fenicsproject) MAC-2:~ lorenzomarta$ cd Desktop/Pre-simulation/

(fenicsproject) MAC-2:Pre-simulation lorenzomarta$ python defDT.py

Traceback (most recent call last):

File “/Users/lorenzomarta/Desktop/Pre-simulation/defDT.py”, line 9, in

mvc_Dxx = MeshValueCollection(“double”, mesh, “meshDxx.xml”)

File “/Applications/anaconda3/envs/fenicsproject/lib/python3.10/site-packages/dolfin/mesh/meshvaluecollection.py”, line 16, in **new**

return mvc(mesh, dim)

RuntimeError:

*** -------------------------------------------------------------------------

*** DOLFIN encountered an error. If you are not able to resolve this issue

*** using the information listed below, you can ask for help at

*** [fenics-support@googlegroups.com](mailto:fenics-support@googlegroups.com)

*** Remember to include the error message listed below and, if possible,

*** include a *minimal* running example to reproduce the error.

*** -------------------------------------------------------------------------

*** Error: Unable to read DOLFIN XML data.

*** Reason: Unable to find tag <mesh_value_collection>.

*** Where: This error was encountered inside xmlutils.cpp.

*** Process: 0

*** DOLFIN version: 2019.1.0

*** Git changeset:

*** -------------------------------------------------------------------------

How can I proceed? I cannot understand the nature of the error. Could it depend on the right directory or not? How can I check if I am in the right ambient?