I can download, install and run jar files on an old Nokia mobile based on midp-1.0

If I do the same without any modifactions on the source code or jar file with a midp-2.0 based Nokia mobile, I always get the error message 'Invalid jar file'. I tried it with the N70 and N80 mobile, the download goes always through bluetooth.

1) Does anybody know this issue and can help me to resolve it?

2) Where can I find further error or log messages on the phone in order to get more information.

Any help is very much appreciated.