I have a friend in The Netherlands who is insistant that when the currency changed from guilders to euros there was a huge mistake made in the calculations, thus causing widespread financial loss to many. Is this true? Can someone shed some light on this for me? Thanks in advance

What does he have to base this on? My sons fiancé visits Canada often and has no discrepancy in changing guilders to CDN dollars at any time and if this were the case, the exchange rate would suffer. No. I think your friend is nuts.

This not true. What happened is that people got disgruntled about the price of things. Whereas things that formerly cost x amount of guilders now should cost x/2 euros (because the change that was made was that all accounts changed from guilders to half that amount in euros) often cost more, i.e. retailers made use of the change to up their prices a bit. So people say: See, things have gotten more expensive due to the change to euros: there must have been a mistake. Actually, it is more like inflation. I still hear people say: Heh, that used to cost 100 guilders and now it is 60 euros! (thinking it should be 50).
I hope that this helps. It is a little bit like a conspiracy idea that spreads like wildfire.