rgl on macosx

Dear prof. Iacus,
I'm a newbie in R, and I'm interested in rgl package, because of my
work on social network analysis (I use sna package, but I would like to
use rgl to plot 3D graphs).
My problem is that I cannot find a way to load it, because the command
library(rgl) gives me this output:

Error in dyn.load(x, as.logical(local), as.logical(now)) :
	unable to load shared library
"/Library/Frameworks/R.framework/Resources/library/rgl/libs/rgl.so":
   dlcompat: dyld: /Applications/R.app/Contents/MacOS/R can't open
library: /usr/local/lib/libpng12.0.dylib  (No such file or directory,
errno = 2)
Error in library(rgl) : .First.lib failed for 'rgl'
Error in .C(symbol.C("rgl_quit"), success = FALSE, PACKAGE = "rgl") :
	C function name not in DLL for package rgl

I try to change

Sys.putenv("DYLD_LIBRARY_PATH"=gsub("/usr/X11R6/
lib","",Sys.getenv("DYLD_LIBRARY_PATH")))

in

Sys.putenv("DYLD_LIBRARY_PATH"=gsub("/Library/Frameworks/R.framework/
Versions/2.0.1/Resources/library/rgl/
libs/","",Sys.getenv("DYLD_LIBRARY_PATH")))

in rgl's .First.lib function, but still get no results. I see that the
path it tries to follow doesn't match with the path that I use (which
is correct), but it's the only clue I can give you.

Can you help me?

thank you in advance,
Simone Gabbriellini

ps: I'm having trouble also with the packages manager, which freeze R
while it tries to load the package (I think that it's in looking for
the documentation of the package but could not find it...)
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