Why am I unable to generate code using Randoop where classes of other Jars are involved?

I'm trying to generate Java unit test cases using Randoop of suppose class ABC. Inside class ABC, I've instantiated the Logger class of log4j as a field and this field is being accessed by a method. I've listed class ABC in myClasses.txt. Now while running the gentests command, I'm getting noClassDefFound error for the Logger instance. Please help if we're missing on something?