Hi,
I think the “Metadata file is invalid” message has no effect on the result, look at this post: SEN2COR tool
Once I got the AttributeError, too. The python code is looking for metadata files with a filename mask like S2A_…L1C….xml. My mistake was to open an image in this folder with QGis. QGis writes automatically a metadata file with the name of the image and *.aux.xml at the end. And of course, this xml file has no attribute ‘attrib’.
So be sure not to write any additional data in your S2A folder.
Regards
Ralf