Some days it just doesn't pay to get out of bed

I just got a "supplimental tax" bill from the county. For some reason they think the house changed ownership, and have reassesed the property at current market rates, instead of the Prop 13 rates. Which, if I had to pay the tax, means I'd need to come up with $1000 by the end of next month. But the house hasn't changed hands, it's still owned by my grandparent's trusts, so I guess I'm going to have to fight city hall to get things fixed.