It's ugly code. There's no need to convert number to string to get its digits, neither there's a need to emulate an array with memory variables in VFP.
The code below (not tested) shows a proper way

lnVal2Test = ln
DIMENSION laR[9]
FOR i=9 TO 1 STEP -1
	laR[i] = lnVal2Test % 10
	lnVal2Test = INT(lnVal2Test /10)
ENDFOR
lnDv = laR[9]
lnSum = (laR[1] * 8) + (laR[2] * 6) + (laR[3] * 4) + (laR[4] * 2) + ;
			(laR[5] * 3) + (laR[6] * 5) + (laR[7] * 9) + (laR[8] * 7)

>Please take a look at the code below:
>
>** the last one is the verify digit
>
>
>LN = VAL (DIRETO.REG)
> endif
>
>
>FOR lnCounter = 1 TO LEN(ALLTRIM(STR(ln)))
>lcVarName = 'lcVarName' + ALLTRIM(STR(lnCounter))
>&lcVarName = INT(VAL(substr(trans(ln),lnCounter,1)))
>ENDFOR
>
>R1 = lcVarName1
>R2 = lcVarName2
>R3 = lcVarName3
>R4 = lcVarName4
>R5 = lcVarName5
>R6 = lcVarName6
>R7 = lcVarName7
>R8 = lcVarName8
>DV = lcVarName9
>
>
>Sum = (R1 * 8) + (R2 * 6) + (R3 * 4) + (R4 * 2) + (R5 * 3) + (R6 * 5) + (R7 * 9) + (R8 * 7)
>
>REST1 = MOD(Sum, 11)
>
>DO CASE
>CASE REST1 = 0
>DV1 = 5
>CASE REST1 = 1
>DV1 = 0
>OTHER
>DV1 = 11 - REST1
>ENDCASE
>
>IF DV1 # DV
>
>= MESSAGEBOX ("invalid code")