Archived:Installing signed MIDlets not supported on Nokia 6600 early firmware (Known Issue)
Signed MIDlets are not supported in the Nokia 6600 software version 3.42.1. The only supported domain is untrusted domain. Thus only MIDP 1.0 MIDlets and untrusted MIDP 2.0 MIDlets can be installed.
No solutions exist for software version 3.42.1, but this issue has been corrected in software release 4.09.1, where 3rd party domain will be supported.