R help - Mar 2011 - Help: creating owin{spatstat} objects from GIS data

Dear R list,

I'm trying to create an object of class "owin" (observation
window) in the
package spatstat from GIS mapping data. Here's an example of my problem.
Everything
goes well until the last line of code. I get the error message shown at the
bottom:
library(spatstat)
library(sp)
library(maptools)
con <- url("http://gadm.org/data/rda/CHE_adm1.RData")
class(con)
print(load(con))
close(con)
SP <- as(gadm, "SpatialPolygons")
W <- as(SP, "owin")

"Error in owin(poly = opls) :
  Polygon data contain overlaps between polygons"

Thanks for any help,
Axel.

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