Hi Guilio,
I have the latest WIP installed (6.0.16152.9051, 05/31/2016), same problem here. With the method you described I nailed it down to one plugin which seems to cause the error: Vipers
http://www.food4rhino.com/project/tangchi?etx (attached as zip).
Can you repeat the error on your machine?
Cheers,
David
vipers_by_tc20160119.zip (323 KB)