Andrew,
You might want to wait for sp3 to come out. It's due anytime now (I think end of July, but your mileage may vary). You can't archive from mailboxes which are over their hard quota. Remember that EV uses the exchange send as/receive as permissions, and if the account is over quota it won't allow those sends/receives. The "temp solution" is to up the quota, do the archive, reset the quota.
micah