This happens to EVERY coin.  If the amount you are trying to send is greater than ~60x the average amount you had incoming then you will get either that error (or sometimes it will attempt to send and get stuck causing panic the first time it happens).  The confusing parts is it is the amount of transactions tied to the amount you are sending that is considered too large...not the amount of MRC.  Example if your incoming amount was on average 1000MRC then you should be able to send 60000MRC in a single transaction.  If it was 1MRC incoming then 60MRC send. etc etc.