regarding assembly routines using in C programming

I need to passing arguments ,parameters passing,
also i need return a value from assembly routine.

I've read a article from keil,ie.,Mixing C and Assembly.In that article,They told create a SRC file,
then modify your SRC file ,What you write in that assembly in SRC ie.,updated.

Thereafter,you assemble Updated SRC file with your c file.

But I,ve got a error
<CLASSES (XDATA (X:0xE000-X:0xFFFF), HDATA (X:0xE000-X:0x13FFE), CODE (C:0x400000-C:0x40FFFF), CONST (C:0x400000-C:0x40FFFF),
ECODE (C:0x400000-C:0x47FFFF), HCONST (C:0x400000-C:0x47FFFF))
*** ERROR L220: INVALID INPUT MODULE MODULE: startup400.obj (?C_STARTUP)>

Actually I've used Dallas 80C400,I allocated off-chip code 0x400000- 0x80000and
off-chip X-Data memory 0x10000- 0x3FFF.

then I put NOVERLAY at LX51misc in MISC control.

I include in my project startupa400.a51-Which is memory defined file(In assembly formaT).
then my C file,then library file of rom400_init.

I don't konw exactly assemble SRC file.Currently I've used Keil-C 2.0 version.

Pls Give Solutions or give your idea to solve this problem.