This is the line that is defining where to save the logfile:
log4j.appender.FILE.File=${log}/logfile.html
If you change that to
log4j.appender.FILE.File=C:/log/logfile.html
Then it might work.
AFAIK, the first line in your config log = C:\Log
have no effect whatsoever. You can't use variables like that in your config file.