I've seen this problem popping up on this board a couple of times. I found a solution to the problem that the Nokia JDK can not be used (class not found errors, browsing for Nokia JDK classes does not work, etc).

In this case, it seems the problem is the installation of the Nokia SDKs before the Mobile Set from JBuilder; an incorrect installation order.

If found this solution:
- Uninstall everyting: Nokia SDK, Mobile Set, JBuilder itself.
- Then, and this is the crucial point: Goto your home directory (e.g. C:/documents and settings/<user-name> under Windows) and manually remove the directory ".jbuilder" entirely! If you re-install JBuilder without removing this directory, you wind up with the same problem over and over again.
- Reinstall everything in the right order: JBuilder, Mobile Set, Nokia SDK.