We've been testing an application in a signed and unsigned state.

Unsigned version worked perfectly. Signed version worked first time, then invalid certificate message was displayed when trying to launch. I've now tried re-installing the app and continually get one of two messages - 'application illegally modified' or 'action failed'.

I've tried factory reseting the phone and then installing mine or other apps, but no apps will now download to the specific device.

The phone in question is a Nokia 6230.

Any help would be much appreciated.