The purpose of this study is to find a safe dose of actinium-225 when it is labeled to HuM195. This will be done with a "phase I trial," in which a preset schedule of doses gets more powerful for each new group of patients as the trial progresses. If too many serious side effects are seen with a certain dose, no one will be treated with a higher dose, and some additional patients may be treated with a lower dose to make sure that this dose is safe. The starting dose of actinium-225 in this study is less than doses that are known to be safe in animals.