L6218E error with inline function.

Hello, Dears
First I say,I'm afraid I don't have good skills writing in English.

Please see my code.
I defined my inline function code at seva.c file.
This is the seva.c file

#include "seva.h"
...
...
__inline void delay_ms(uint32_t ms)
{
        register uint32_t i = ms;
        for ( ; i ; --i )
        {
                delay_us(250);
                delay_us(250);
                delay_us(250);
                delay_us(250);
        }
}
__inline void delay_us(uint32_t us )
{
    register uint32_t i = us;
        for (; i; --i)
        {
                __NOP();
                __NOP();
                __NOP();
                __NOP();
                __NOP();
                __NOP();
                __NOP();
                __NOP();
                __NOP();
                __NOP();
                __NOP();
                __NOP();
                __NOP();
                __NOP();
                __NOP();
                __NOP();


        }
}
...
...

and I declare function prototypes at seva.h file.
seva.h

...
...
__inline delay_us(uint32_t us);
__inline delay_ms(uint32_t ms);

when I try to call these delay functions in main.c file.
main.c

#include "seva.h"
...
...
void main(void)
{
   P04 = 1;
   delay_us(100);
   P04 = 0;
}

As you guess, It cause L6218E error.
and I found http://www.keil.com/forum/13177/ this column.
I defined every my inline code from seva.c to seva.h file.
and It works well(means no compile error).

But there is one thing still confused..
See, Next code.
seva.c

...
...
__inline void delay_loop1( )
{
    register uint32_t i = 500;
        for (; i; --i)
        {
                __NOP();
        }
}
...
...

seva.h

...
...
__inline void delay_loop1(void);
...
...

and I call this function at main.c file like above.
but It doesn't have any comfiler errors.
As I think, the difference delay_loop1 function and delay_ms function is only whether has parameter or not.

please tell me why delay_loop1 function compile without error, and why inline function has parameter occur errors.

Did you understand what I try to saying? I think I wrote too difficult.

Thanks for reading.