I vote this.
There's no question that it's a forceout and an error. The only debate is whether to assign the error to the SS or 1B. ... IMO, you don't assign errors because fielders are not where you, the scorekeeper, think they should be. Rather, you judge the throw based on where the fielder actually is. Given the position of the first baseman, it was a bad throw.
There is an excption to this rule. If a cacther throws down on a steal but nobody covers the bag and the runner advances to 3rd the error can be charged to the 2B/SS who was responsible for covering the bag. At least I think that is an exception. Otherwise I agree with it whole heartedly.