got message 'an array dimension must be an integer between 1 and 1000

Got this message first time running the report for larger time and data. How to debug this? halt on this statement

"  redim preserve a[c];"

shared stringvar array a;

local stringvar t := {CLSPAYTP.OTORD#};

shared numbervar c:=c;

shared stringvar ords:=ords;

//if instr(ords,{CLSPAYTP.OTORD#})<=0 then

    ords:=ords & ',' & {CLSPAYTP.OTORD#};

if not(t in a)

then (

        c:= c + 1;

        redim preserve a[c];

        a[c] := t;

);

if c > 0 then a[c]