some (good) system admins disable some funcs in shared hosting environments to limit potential security risks. It is also possible that safe mode is enabled.
what this means is you will not be able to programmatically make directories or change permissions, (as well as other things such as include a file located outside your base directory) you'll have to do it manually.
there may be a way around this, but I am not aware of one. realize though that this is a benefit, not a hinderance - from a security standpoint.
