help with JAR files!!

hi!
i have a N3230 phone.
i have a problem with installing JAR files.
everytime i try to install a *.jar file i get
Installer: System Error (-12)
i found on the internet that -12 means
'directory not found' for something like that.
i get this error even with *.jar files that
some time ago i installed without any problems!
i checked wether i have enough free space, so
disk C: has ~2mb free, and disk E: 1 MB free (256MB MMC).
so i think its enough for a ~60kb java application
i also tried installing sis files, these install without any problems.
so what could it be, and how can i repair it?
thnx in advance guys! 😊