Bloo,
It sounds like the user that owns the MY_PACKAGE package is not the same as the user that is trying to access it from your
java code. So either change the user in your java code, or grant permission for other users to access MY_PACKAGE. Note that if you choose the second option -- granting permissions to other users to use MY_PACKAGE -- then in your java code
you should prefix your call to MY_PACKAGE with the name of the user that owns the package, for example:
Good Luck,
Avi.