I have processed all night and then this morning I tried to process a new tile and got the error
Sentinel-2 Level 2A Processor (Sen2Cor), 2.4.0, created: 2017.06.05 started ...
Cannot create the config object configPic.p, parent folder may be write protected.
I have checked, there is nothing strange on rights in either the script or the destination. I am admin but I am reluctant in firing a script as a super user. So was a bit stuck.
My hack was that I went into the destination folder and ran the command and this worked
/media/julien/NuDrive1/WorkInProcess/Chris/Latitude_hill$ L2A_Process S2A_MSIL1C_20170731T012721_N0205_R131_T52JDR_20170731T013300.SAFE/
This is strange, is it the way the paths are called? Of course the root '/media' is not accessible, it is the same error like if the script tried to write there.
So the command needs to be started from the folder containing the data folder (at least in my case).
Hope this help.