I got the same problem (with a new sen2cor installation on a new machine).
After fiddling around for a long time, I apparently now “solved” it by going back to that precise pytables version which I used on another machine successfully (installed month ago). It seems that sen2cor/L2A_Tables.py of sen2cor 2.1.1 struggles with the newer pytables version meanwhile included in Anaconda2.
After struggling with various errors, I have now come across this particular one but I have pytables 3.2.2 and the downgrade command says version 18.104.22.168 no longer exists: Package missing in current win-64 channels. Is there another way to downgrade?
I have got that bug too. The command provided by Markus works and solves the issue for me.
I then had another one : AttributeError: ‘bool’ object has no attribute ‘Size’ which was solved by removing the L2A product whose generation had failed.