This problem is usually caused by a bad file in your data folder. On vista it may also be caused by a feature called Data Execution Prevention.
To fix this :
- in your Gravity/RO/ folder delete or rename the folder called "data"
For vista users, to turn off DEP :
1. Open the Windows Control Panel
2. Click on System (if you do not see this, click on classic view on the top left)
3. now click on Advanced System Settings
4. In the Advanced tab, click on Settings.. under Performance
5. In the Data Execution Prevention tab select Turn on DEP for all programs and services except those I select :
6. In the list add the EssenceRO executable and EssenceRO patcher executable.
7. Press Apply/Ok everywhere and you are done!