There is a minor bug in "Nokia Developer's Suite 2.0 for J2ME" that had me on a wild goose chase.
If the JAR and JAD files are in a folder whose path has an apostrophe character in it (e.g. "Tim'sTest"), an error is produced when the "Create Application Package" option is chosen, then "Generate..." is clicked. The error is that the .class file in the system-created "preverified-temp" folder can not be found (this folder is created, but is empty).
Note that when the apostrophe is in the actual JAR and JAD file names, rather than the folder name, no error occurs.