IAR Workbench Error[Pe159] beim kompilieren

Hallo,

ich beginne gerade mit IAR Workbench und hab mit den unten gezeigten 
Zeilen begonnen
und bekomme folgende Fehlermeldung:
"Error[Pe159]: declaration is incompatible with previous "RCC_Setup" 
(declared at line 5) ........"

HIer mein main.c:
#include "stm32f10x_lib.h"

int main()
{
 RCC_Setup();

 // return 0;
}


void RCC_Setup(void)
{
    // RCC system reset(for debug purpose)
    RCC_DeInit();
    // Enable HSE
    RCC_HSEConfig(RCC_HSE_ON);
    // Wait till HSE is ready
    while(RCC_GetFlagStatus(RCC_FLAG_HSERDY) == RESET)
        {;}
    // Enable Prefetch Buffer
    FLASH_PrefetchBufferCmd(FLASH_PrefetchBuffer_Enable);
    // Flash 2 wait state
    FLASH_SetLatency(FLASH_Latency_2);
    // HCLK = SYSCLK
    RCC_HCLKConfig(RCC_SYSCLK_Div1);
    // PCLK2 = HCLK
    RCC_PCLK2Config(RCC_HCLK_Div1);
    // PCLK1 = HCLK
    RCC_PCLK1Config(RCC_HCLK_Div1);
    // Select HSE as system clock source
    RCC_SYSCLKConfig(RCC_SYSCLKSource_HSE);
    // Wait till HSE is used as system clock source
    while(RCC_GetSYSCLKSource() != 0x04)
        {;}
    // Enable PBs GPIO clock


   RCC_APB2PeriphClockCmd( RCC_APB2Periph_GPIOA | RCC_APB2Periph_GPIOE,
                          ENABLE );

}

eingebunden sind: cortexm3_macro.h, stm32f10x_conf.h, stm32f10x_flash.h, 
stm32f10x_gpio.h, stm32f10x_lib.h, stm32f10x_map.h, stm32f10x_nvic.h, 
stm32f10x_rcc.h, stm32f10x_type.h

bitte um Hilfe