I ended up purchasing SpeedFinish
(http://www.custombuildingproducts.co...eedFinish.aspx)
- a quick drying cement based floor patch. It did the trick and
allowed me to return the underlayment and screws saving me about $150
not to mention the labor. The floor went down fine. Only warning, when
they say SpeedFinish is quick drying, they mean it. You only want to
mix the amount you can work with in 10 minutes. Thanks for the replies.