Less than three weeks after the departure of its CFO, H&R Block, Inc. said this morning that CEO Mark Ernst has resigned as the company looks to restructure amid mounting losses from its subprime lending unit Option One Mortgage Corporation. Here is the full press statement. The Associated Press reports:

H&R Block Inc. said Tuesday that Mark Ernst has resigned as chairman, president and chief executive of the tax preparation and accounting services company. He is being replaced as chairman by former Securities and Exchange Commission boss Richard Breeden, who led a dissident shareholder group that won three seats on the board. Former Aetna Inc. executive Alan Bennett was named interim CEO while H&R Block looks for a permanent replacement. H&R Block shares slipped 10 cents to $18.97 in morning trading.

The tax preparer has seen its proposed sale of Option One cast into doubt as the mortgage industry has continued to slip further into the doldrums.