Because Arwen is in Beta, we’ve temporarily limited the amount of coin you can lock in escrow and trade. Currently, each escrow you can open with Arwen is limited about $100 USD worth of coin, and each trade is limited to about $20 USD worth of coin. The number of escrows that may be open at the same time, by a single user, is also limited during this Beta period.  These limits will be raised over the course of the Beta period.