R_x11.so

Hi the list,

I just installed  the R-1.7.0-1mdk.i516.rpm package on a mdk 9.1. All 
looks fine until I try to launch some graphics functions as png() or 
even demo( graphics). I receive the following example message:

 > png()
Error in png() : R_X11 module cannot be loaded
In addition: Warning message:
unable to load shared library "/usr/lib/R/modules/R_X11.so":
  /usr/lib/R/modules/R_X11.so: undefined symbol: png_set_IHDR


Also I verified that this file exists and it is.
~/>updatedb
~/>locate "R_x11.so"
~/>/usr/lib/R/modules/R_X11.so

Which variables have to be configured ? How can I do since I installed 
an rpm ?


Is there somebody who could help me.
In advance thank you.

Greg