Raja,

Sounds like you are running the actually executable file rather than
the shell script that is supplied in the distribution. If you look in
the "gap/bin" directory, there is a shell script which has a bunch of
paths declared in it, followed by a line running the gap executable
with a list of arguments (including this -l <libname> one).

Make sure the paths reflect your installation and run the script
instead.

Cheers,
Michael.