[Rivet] Sherpa+Rivet: m_io->fill_next_event fails

[Hendrik Hoeth]

Thus spake Eike von Seggern (jan.eike.von.seggern at physik.hu-berlin.de):

> Okay, it's not a Rivet problem and it's not a problem with asymmetric
> beams either. I've attached a tool that just reads in HepMC and prints
> out the event numbers.

Can you put a couple of events (100 or so) as HepMC file on hepforge,
please? Or check if there are events with cross-section error = nan?

-- 
"Two equal numbers are equivalent, even if they come from two
 different people one of which you don't like"
(MLM about the theoretical top cross-section, in a meeting
about theoretical uncertainties on the top mass)