The issue could be caused by the incorrect procedure or adding/removing currencies in osCommerce 2.2RC2a. To resolve it please do the following:
1. Go to administration panel and click ‘Localization’->’Currencies‘.
2. Then add a new currency with the following settings:
Name: ‘US Dollar’;
Symbol Left: $
Decimal Point: .
Thousands Point: ‘
Decimal Places: 2
3. Make it default and click Update currencies.
4. Then select your new currency and make it default. Update currencies.
5. Now you are free to remove the ‘US Dollar’ currency.