Too many commands in a transaction

Hi
ERROR: cannot have more than 2^32-1 commands in a transaction
SQL state: 54000
Iam getting the above error when iam running my program. 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