git-p4 submit, Can't clobber writable file

I followed the instructions at http://modular.math.washington.edu/home/mhansen/git-1.5.5.1/contrib/fast-import/git-p4.txt

But, I am not able to git-p4 submit. Any idea?

git-p4 clone //build/scripts build_scripts cd build_scripts vi foo.h git commit foo.h git-p4 rebase git-p4 submit

  from sets import Set;
Perforce checkout for depot path //build/scripts/ located at /home/gyang/workspace/build_scripts/
Syncronizing p4 checkout...
//build/scripts/foo.h#1 - added as /home/gyang/workspace/build_scripts/foo.h
Can't clobber writable file /home/gyang/workspace/build_scripts/foo.h
//build/scripts/foo.c#1 - added as /home/gyang/workspace/build_scripts/foo.c
Can't clobber writable file /user/home/gyang/workspace/build_scripts/foo.c
......
command failed: p4 sync ...

Thanks.