When you commit a new file to a subversion repo, the file permissions associated with the file become "set" in the repo.
When some-one else checks out that same file, it will have the same permissions.
If the file is meant to be run as an executable script, the user (you or some-one else) will need to use chmod to change the file permissions before they can run it.
You can fix this by using svn propset to change the properties associated with a file after committing it to a repo.
For example, let's say you checked a script called myScript.py before chmod'ing it to executable.
See the documentation here: http://durak.org/sean/pubs/software/version-control-with-subversion-1.6/svn.ref.svn.c.propset.html.