Error when running program for no purpose

Im making a program for my AP Computer Science in school and when i downloaded TxT pad at home and i installed the jdk-1_5_0_04-nb-4_1-win update, the same one we used at school it gives me a problem. Everything compiles fine and when i got to run the application is get the error:

Exception in thread "main" java.lang.NoClassDefFoundError: NumberConvert

I have no clue why this happened and really no idea about how to fix it...i could use some help plz.

Thanks.

[489 byte] By [Tyrant27a] at [2007-10-2 0:45:10]