I'm sorry to resurrect this old post, but i had the same problem, and there was nothing on the net about it.
I'm using JBuilder 8 (Personal edition), and i solved the problem by:
I went Project->Project Properties->Required Libraries
The library I added was classes.zip, found in c:\nokia\devices\nokia7210\lib this fixed the problem, (you could use another emulator classes.zip if you wanted.)
dunno if it's how
you should do it, but it worked for me.