java.lang.NoClassDefFoundError

Why is it that like 1% of the time I run my program, I get this error? In addition, I sometimes get a FileNotFound Exception for one of the txt files around 1% of the time. Is it that the process of creating the executable jar file is not consistent, or does the file get corrupted? how does this happen?

Note: this is not just a matter of me not including the classfile in the jar or not including the txt file because it works most of the time.

Thanks

[472 byte] By [Nethera] at [2007-11-27 7:29:50]