class not found error

hey frnds,

i m getting the following error evertime i run ne java prog.

Exception in thread "main" java.lang.NoClassDefFoundError:'filename'

my class path is: C:\Program Files\JavaSoft\JRE\1.3\lib\ext\QTJava.zip;

it was working a few days ago, dont know what happend now.

please help....

[326 byte] By [uditBa] at [2007-10-3 4:28:29]