Arduino S-Function 'NO REGS'

Hello guys,

i created a S-Function in Simulink that receives the signal of various sensors measured on an Arduino Mega and send their values via SPI to a 4Duino to be saved to a sd Card.

The function works perfeclty as long as i have less then 8 Inputs. If i add some more Input i get the following error:

rcreceive.c:2235:1: error: unable to find a register to spill in class 'NO_REGS'
 }
 ^
rcreceive.c:2235:1: error: this is the insn:
(insn 4193 4190 4196 437 (set (mem:QI (post_dec:HI (reg/f:HI 32 __SP_L__)) [0 S1 A8])
        (subreg:QI (reg/f:HI 1872) 1)) rcreceive.c:2169 1 {pushqi1}
     (expr_list:REG_ARGS_SIZE (const_int 3 [0x3])
        (nil)))
rcreceive.c:2235: confused by earlier errors, bailing out
gmake: *** [rcreceive.o] Error 1

Is there a Limit of Inputs one can use in a S-Function block? Or what is the reason for this error?

EDIT: The Input Signals are all int16.