install R packages--sorry last letter that I sent I had an error, this one is the right one

Dear All,
 
When I tried to install R packages I found this error:

library(survival)

Loading required package: splines

install.packages("splines")

--- Please select a CRAN mirror for use in this session ---
Warning message:
package splines is in use and will not be installed 

But I just opened R, and haven't used anything yet, how come did it say "package splines is in use"?
 
Thanks
 
Jia