This error can occur if the DI-API has been corrupted. Please do the following:
- In windows, go to Start > Run
- Type in %temp%. and press OK
- In the window that appear locate the SM_OBS_DLL folder and rename it to oldSM_OBS_DLL
- Restart SAP Business One
If this does not solve the issue you should uninstall the DI-API and reinstall it. After that redo the steps above.