problems with clipboard

Hi I'm a mac user. I have problems loading data from mac excel in R.
I'm using these script:

library(utils)
data2 <- read.table(file("clipboard"), header =T, sep ="\t")

____but this is the message that I have from R_____
Error in open.connection(file, "r") : cannot open the connection
In addition: Warning message:
In open.connection(file, "r") :
  clipboard cannot be opened or contains no text

More complicate then that is that sometimes it works sometimes no....... 
I'm very confuse.... any help?

Jamie

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