Cannot export data to a file in R (write.csv)

I am trying to export data in R to a csv file, and as much simple as I try to do it, I always get the same error message. Example:

I create a simple data vector to export

 x <- c(1,3,4,3,5,7,5,8,2,5,7)

I try to export with:

write.csv(x,file='whatever.csv')

And I get an error:

error in file(file ifelse (append a w )) cannot open the connection
In addition: Warning message: In file(file, ifelse(append, "a", "w")) :
cannot open  file 'whatever.csv': Permission denied

How can I solve this?