To fix this, try refreshing your ActiveSync settings,
- Open TouchDown. The Main screen displayed.
- Tap Menu button and select Settings.
- Tap the Connection tab.
- Tap the ActiveSync... button.
- Choose "Refresh ActiveSync Settings."
- After you've completed this operation, go to the first tab marked "Account" and rerun the Quick Configuration wizard.
This should get you back on track and receiving mail regularly.