cannot run java applet

several users who cannot download and run java applet on our WebReflections (v3.0) No commonalities in users – 2 XP, 1 Win98, 1 Win2k for instance. All current IE versions. Get blank HP Remote screen, applet will not load. Following error msg onjava log:

java.lang.noclassdeffounderror:com\WRQ\jpm\defaultsecure