Keil5 cant locate rtl.h, but generates hex file

After getting the new keil5 MDK, i compiled the code developed in keil4. (the legacy package has to be installed to achieve the reverse-compatibility).

everything seems to be working fine, except two change:

#define MHZ             *10000001

#define SYS_FREQ 60 MHZ

#if   SYS_FREQ == (120 MHZ)
        #define SDRAM_PERIOD          8.33  // 96MHz
#elif     SYS_FREQ == (96 MHZ)
        #define SDRAM_PERIOD          10.4  // 96MHz
#elif   SYS_FREQ == (72 MHZ)
        #define SDRAM_PERIOD          13.8  // 72MHz
#elif   SYS_FREQ == (60 MHZ)
        #define SDRAM_PERIOD          16.67  // 72MHz
#elif   SYS_FREQ == (57 MHZ)
        #define SDRAM_PERIOD          17.4  // 57.6MHz
#elif SYS_FREQ == (48 MHZ)
        #define SDRAM_PERIOD          20.8  // 48MHz
#elif SYS_FREQ == (36 MHZ)
        #define SDRAM_PERIOD          27.8  // 36MHz
#elif SYS_FREQ == (24 MHZ)
        #define SDRAM_PERIOD          41.7  // 24MHz
#elif SYS_FREQ == (12 MHZ)
        #define SDRAM_PERIOD          83.3  // 12MHz
#else
        #error Frequency not defined
#endif

//The MHZ (in sdram.h) has to be separated by a white space from the number value,
// unlike in keil4 where the white space was not necessary. 



#include <rtl.h>    // Marks a red cross adjacent to this line in the FileConfig.h only (which is the new way of keil to highlight the warnings and error)
// the error reads : RTL.H File not found with <angled> include; use "quotes" instead

not sure why this error is shown only in the 'file_config.h'. In all the other .c source files, this error is not displayed. also the project is build and i can download and debug the code (though i have not single stepped through whole code, but think that it may not be an issue of much concern)