issue loading doBy library

Hello,

How can I fix this? I have the latest version of R 2.13.2 and I use Mac OS X 10.7.2

library(doBy)

Loading required package: lme4
Error in dyn.load(file, DLLpath = DLLpath, ...) : 
function 'cholmod_l_start' not provided by package 'Matrix'
Error: package 'lme4' could not be loaded

library(lme4)

Error in dyn.load(file, DLLpath = DLLpath, ...) : 
function 'cholmod_l_start' not provided by package 'Matrix'
Error: package/namespace load failed for 'lme4'

TIA,
Best regards,
Giovanni