for a subject on my faculty I need to install JFlex and I found this problem when I downloaded and tried to run it.
~/jflex-1.5.0/bin » ./jflex -h
Error: Unable to access jarfile ./../lib/JFlex.jar
~/jflex-1.5.0/bin » ls ../lib/
java-cup-11a.jar jflex-1.5.0.jar jflex-mode.el jflex.vim
Inside ~/jflex-1.5.0/bin/jflex(and also jflex.bat) you're calling:
$JAVA -Xmx128m -jar $JFLEX_HOME/lib/JFlex.jar $@
I hope you can fix this problem quickly.