Too many commands in a transaction

Hi
Iam getting the below error when iam running my program.
ERROR: cannot have more than 2^32-1 commands in a transaction
SQL state: 54000
If iam not wrong this error ocuurs when there are too many statements executing
in one single transaction.
But this error is occuring in a function that iam least expecting it
to occur in. The function it occurs in is as follows:
BEGIN
        resultindex := 1;

        -- Go through summedprobs, find where rnum falls, set resultindex
        FOR i IN REVERSE (array_upper(summedprobs,1)-1)..1 LOOP
                IF rnum >= summedprobs[i] AND rnum <= summedprobs[i+1] THEN
                        resultindex := i;
                END IF;
        END LOOP;


        RETURN (dobs[resultindex]);
        EXCEPTION  WHEN program_limit_exceeded THEN
                RAISE NOTICE 'Exception in GETRES';
        RETURN (dobs[resultindex]);
END;


Is is beacuse of the REVERSE command? or because the program is
executiung many select and update statements?
Catching the exception isnt helping here either.Can anyone explain me
why  this error occurs and what i can do to resolve it?


Thanks
Sam