Does the user local have permissions to access the folders in the path to the file? Just because it has permissions on the file doesn't mean it can access the file.
as user main, try
su local
<enter password>
touch /home/main/some/folders/script
To solve it, you'll need to
chmod g+rx each directory in the path
(Note that to run a script, the user doesn't actually need read permissions, on a directory, just execute permissions.)
