From Forum Nokia Wiki

This attached ZIP file (File:HelloWorld VeriSign.zip) contains a HelloWorld MIDlet, which has been signed with VeriSign certificate.

If you have problems in installing your VeriSign signed MIDlet on the phone, test with this MIDlet. If you can install this one, there is something wrong with your signing, or your have forgotten to add the required permissions attributes on the JAD file, or....

If someone has a Thawte code signing certificate at his disposal, it would be great if you could sign this MIDlet with Thawte certificate too (the whole NetBeans project has been included in the ZIP file so you can see that the MIDlet does not contain anything malicious). As first step, please sign the MIDlet using an unsigned JAD file. In the next step we can then work on getting a MIDlet signed with two different certificates...