yeah from a SQL perspective, an update that affects zero rows is not an "error", but from your perspective it's a logical error, as you expected at least one row to be fiddled with. probably want to check the rows effected with @@rowcount to be sure whether your statement affected anything; are you doing that now?

show us your real code you are using; it might be something minor in your vb6 code you are overlooking, like assigning a value to a variable, or not substituting a value into your UPDATE statement.