impossible install. download not successfull

I have a nokia 6600 and when I try to install java
application (for example .jad or .jar games) It give me
the "impossible install. download not successfull" error.
I'm not so good in English and I'm not sure that is the
right traslation from the Italian "impossibile installare.
download non riuscito".
By the way if you could tell me how to solve the problem I
will be very gratefull.
Thanks in advance
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Caminante no hay camino, se hace camino al andar. Juan (de
Madrid)