I got it !
it works ..
my error was the missing brackets on the I2CREAD command
it seems that without the bracket the I2CREAD become a I2CWRITE !

I try using address $C2 or using a constant ... same results
thanks to everybody
francois

here is my HUGE code !
'*******************************************
'* Name : TX2300 avec 16F84 *
' Variable Definitions
SCL var PORTA.4
SDA var portA.3
LOCKBYTE var byte

Main:
I2CWRITE SDA,SCL,$C2,[$48,$F8,$AE,$FF],errorload
LOCK:
pause 100
I2CREAD SDA,SCL,$C2,[lockbyte]
Lcdout $FE, 1 ' Clear LCD screen
pause 50
lcdout "lock=", #lockbyte, " bit=", #lockbyte.6
pause 1000
goto lock

errorload:
Lcdout $FE, 1 ' Clear LCD screen
pause 50
lcdout "error load "
pause 1000
goto main