Some googling found that others had had the same issue. One poster said how they had fixed the problem by disabling the Wifi positioning option (one of the upgrades in 3.04). My phone would crash before I had time to make any changes to the Ovi setup.
I did have a stroke of luck. I opened the "Application mgr" in the Settings menu and found there was an application there for WiFi positioning, I uninstalled this and Ovi maps worked without causing the phone to crash.
Has anyone had a similar problem? How did you fix it?