Actually, you do NOT have a problem with FTP transfer. FTP batch jobs (when using the IBM TCP/IP component) have EXEC PGM=FTP so you are executing some vendor (or home-grown) program instead to do the file transfer. As such, you need to read the vendor documentation, or contact the vendor directly, about what is needed to accomplish your goal.
The error messages you are seeing indicate that SMS is managing the storage pool, looking for space for your GDG generation, and not finding it. Whether or not YOU think there is space in the storage pool, SMS cannot find enough space. This may be due to large primary space allocation or some other factor -- but, again, this is an issue only the manuals or vendor of the package can help you with.