[Gm2] can only CAST objects of the same size

[Vladimir Karpenko]

Hello, EveryBody,

        I am trying to count something with gm2 here. Code looks something like that:
        PatternHash:=(PatternHash*Base+LONGCARD(ORD(FetchChar(Pattern, Index)))) MOD 
Prime;
        and like that:
        TextHash:=(TextHash*Base+LONGCARD(ORD(FetchChar(Text, Index)))) MOD Prime;
        and like that:
TextHash:=(TextHash+Base*Prime-LONGCARD(ORD(FetchChar(Text,Index)))*Power) MOD 
Prime;
        and like that
        TextHash:=(TextHash*Base+LONGCARD(ORD(FetchChar(Text, Index+PatternLength)))) 
MOD Prime;

        on every of the lines mentioned above i got some strange error: 
        "can only CAST objects of the same size"

        FetchChar looks like that:
PROCEDURE FetchChar(Source:String; Index: CARDINAL):CHAR;
BEGIN
        IF Index>Length(Source) THEN
                RETURN "|";
        ELSE
                RETURN Source[Index];
        END;
END FetchChar;
And string:
TYPE String= ARRAY [0..255] OF CHAR;
What should i do? Where am i wrong?

Thanks, Vladimir.