i'm getting an error when i try assembling this.. i'm using nesasm3

i get the message "Incorrect addressing mode!" for both ( STY $F1,X ) and ( STY $F9,X ).. anyone know why?

**Code:**

LDX #$01

REAP:

LDA $04,X

TAY

EOR $F9,X

AND $04,X

STA $F5,X

STY $F1,X

STY $F9,X

DEX

BPL REAP

REAP:

LDA $04,X

TAY

EOR $F9,X

AND $04,X

STA $F5,X

STY $F1,X

STY $F9,X

DEX

BPL REAP

i get the message "Incorrect addressing mode!" for both ( STY $F1,X ) and ( STY $F9,X ).. anyone know why?