help using irregular polygons R with spatstat package

I'm trying to test for conspecific attraction with snowy plovers, 
in other words, aggregation in response to successful nest fates.  
I have nest locations, fates, and polygons of potential nesting 
habitat.  The polygons of potential habitat are from barrier 
islands in Florida.  Most of the polygons are ~7km in length and 
200-300m wide.  All data was read into R as shapefiles created 
with ArcMap 9.2.

I have loaded the following libraries in R: sp, rgdal, spatstat, 
and maptools.

I've used essentially the following code (substituting my actual 
files):

boundary=readOGR(dsn="polygon.shp",layer= "polygon")
nests=readOGR(dsn="nest.location.shp", layer="nest.location")
boundary.owin=as(as(boundary,"SpatialPolygons"),"owin")
nests.points=as(nests,"SpatialPoints")
nests.ppp=as.ppp(nests.points,W=boundary.owin)

All script works fine except for the last line.  When I run this 
one, I get the following error:

Error in as.ppp.SpatialPoints(nest.points, W = boundary.owin) :
  unused argument(s) (W = list(type = "polygonal", xrange = 
c(252580.626188745,.........

Does anyone know what this error message means?  And suggestions 
on what I can/should do????

Thanks!
Raya


--
Raya A Pruner - Graduate Student
University of Florida
Department of Wildlife Ecology and Conservation
PO Box 110430
Gainesville, FL 32611-0430
352-214-3262