sy-subrc 801

I have written a program to simply strip the timestamp off ftp'd files.

I identify the filename and the use 'SXPG_COMMAND_EXECUTE' to call a custom command ZMV which calls the OS mv command to rename the file. I have tested this in my test environment, but when I moved to production, the program runs, but returns an 801 and the files are not renamed. Google hasn't been very helpful on this one. Anyone know what my issue is?