If you define this variable, the FTPDLX file transfer routine (used by ATE implicitly and by A-Shell/Windows when you explicitly call FTPDLX) will output detailed, low-level debugging information to the file %temp%\ftpdebug.log (prior to A-Shell build 1153 of June 2009, the log file was named c:\debug.log). Note that even without this, a somewhat higher-level debug log of the last file transfer can always be found in the file ftpdlx.log (in the current directory.)