Louise Robbins bought shares in an exchange traded fund last Friday afternoon as markets fell, knowing that she had enough money in her Vanguard Group settlement fund to pay for the trade.

Tuesday morning, the 60-year-old Boston book editor received an erroneous email saying her settlement account did not have sufficient funds to pay for the transaction. A Vanguard spokesman confirmed that other retail clients received similar messages and the problem would be resolved without customers having to take any action.