The rates that Rusoro quotes are the "parallel" or market rates, which must be used if one is not registered to purchase US dollars at the official rate from the government. This results in a currency translation loss.
Crystallex noted this issue in its last two quarterly reports. In an e-mail from RM a while back I was told that Crystallex was in process of applying for registration to purchase at official rates, but I would guess that issue is not yet resolved.
Apparently, there is not a lot of foreign currency available at official rates and most companies take this hit when repatriating money back home.