Probleme d'exécution

PROGRAM tautogramme;
USES WINCRT;
VAR
ch:string;

function tauto(ch:string):boolean;
var
pc:char ;
i:integer;
t:boolean;
begin
pc:=upcase(ch[i]);
t:=true;
i:=1;
repeat
i:=i+1;
if(ch[i]=' ') then
if(i+1<=length(ch))then
if(upcase(ch[i+1])<>pc)then
t:=false;
until(t=false)or(i=length(ch)-1);
tauto:=t;
end;

BEGIN
readln(ch);
if tauto(ch)then
write('tautogramme')
else
write('non tautogramme');
END.

tauto caused a stack fault in module tauto.Exe at 0001:00:29 qui peut m'aidez ??