Try to download the updated version of the Nokia Store by visiting www.store.nokia.com. It should prompt you if you want to update your Nokia Store application on the phone. If issue is still the same, you can do the following:
1. Restore Factory settings> Menu > Settings > Restore factory sett. .>Settings only. The default code is 12345 unless otherwise changed. Personal data will not be affected.
2. Check for any available updates. If none, reinstall the software using the Nokia Suite.