Ask a question about loading the module: An error occurred in insmod!

Ask a question about loading the module: An error occurred in insmod! -- Linux general technology-Linux programming and kernel information. The following is a detailed description. This is a simple Start Program for driver learning:
// Hello. c
# Include
# Include
MODULE_LICENSE ("Dual BSD/GPL ");

Static int hello_init (void)
{
Printk (KERN_ALERT "Hello, world \ n ");
Return 0;
}

Static void hello_exit (void)
{
Printk (KERN_ALERT "Goodbye, cruel world \ n ");
}

Module_init (hello_init );
Module_exit (hello_exit );

I will not explain the program ......

Makefile

Obj-m: = hello. o
KERNELDIR: =/lib/modules/2.6.20/build
PWD: = $ (shell pwd)
Modules:
$ (MAKE)-C $ (KERNELDIR) M = $ (PWD) modules
Modules_install:
$ (MAKE)-C $ (KERNELDIR) M = $ (PWD) modules_install
If all of the above are complete, this error will occur during make.
Shana @ shana :~ /Linux _ driver development $ make
Make: There is nothing to do for 'modules '.
The reason is very simple. You must have copied it from me ~~~ The Makefile format is incorrect ~

They all follow the steps of others. Why is the error:
Insmod: error inserting './hello. ko':-1 Invalid module format
What's wrong with this?