Resolution:
Follow these simple steps to troubleshoot your custom FTP script implementation

1> Make sure you have detailed tracing turned ON.
2> Copy the attached sample repository to your local machine
3> Make sure you have set the custom Java classes in the classpath and you have copied the user defined properties file in the &ltBC>/resource directory.
4> Start &ltBC>/bin/ProcessDesigner and open the repo from step 1
5> Review the script "Custom FTP Script" in the process "Custom FTP Script Test"
6> Modify it as per your needed (or copy your script instead)
7> save and run it in debug mode

bc-trace will have detailed trace that includes the FTP script tracing.