BTW, we are now centralising materials file at a Git repository. Now it is possible to include http remote ENTITYs inside the GDML file.
Instead of propogating and modifying materials.xml file on local systems, as it was the case till recently, we should try now to maintain a common one, i.e. by using this in our GDML files:
<!ENTITY materials SYSTEM "https://sultan.unizar.es/materials/materials.xml">
That way, if there are issues/errors with any material definitions we fix those issues for anyone.