tcl/tk problem

I have JUST started using R.  I am using R 2.0.1 on a mac (os x) to  
run another program (called GRASPER, Generalized Regression Analysis  
and Spatial Prediction for R).  When I try to run Grasper, I get an  
error for tcl/tk:

 library(grasper)

Loading required package: mgcv
This is mgcv 1.1-8
Loading required package: MASS
Loading required package: tcltk
Error in dyn.load(x, as.logical(local), as.logical(now)) :
	unable to load shared library  
"/Library/Frameworks/R.framework/Resources/library/tcltk/libs/ 
tcltk.so":
  dlcompat: dyld: /Applications/R.app/Contents/MacOS/R can't open  
library: /usr/X11R6/lib/libX11.6.dylib  (No such file or directory,  
errno = 2)
Error: .onLoad failed in loadNamespace for 'tcltk'
Error: package 'tcltk' could not be loaded


However, tcl/tk appears to be there:

 capabilities()

    jpeg      png    tcltk      X11    GNOME     libz http/ftp  sockets
    TRUE     TRUE     TRUE     TRUE    FALSE     TRUE     TRUE     TRUE
  libxml     fifo   cledit  IEEE754    bzip2     PCRE
    TRUE     TRUE     TRUE     TRUE     TRUE     TRUE

Does anyone know of a solution to this?

Thanks,
Jennifer Skene