I tried this quickly now and it seems to work here atleast out of the box:

@girish I have a 238 ko iCal file. I've split it in twice and I went from 250 importation err from 1 err. The problem should come from that, thanks! I was at the beginning thinking about it (splitting the file) but after that, I was focusing on RateLimit - wrong way! Also, I advise people which want to import a big file to increase drastically the mem allowance of the app (2Gb in my case)