How to this SAS transport file in R?

Dear All, 

I try to read the SAS transport file in R, but it shows error. Please help!
I am using R 2.11.1 

library(foreign) 
download.file("http://isites.harvard.edu/fs/docs/icb.topic35387.files/demo_c.xpt","C:/Desktop/demo_c.xpt") 
sasxport <- read.xport("C:/Desktop/demo_c.xpt") 

Error in lookup.xport(file) : file not in SAS transfer format

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