Error message

I suddenly started getting the error message below.
Not sure why.? If I type intalled.packages() it
shows Matrix and lme4 installed.? Can someone tell 
what's going on and what I need to do to remedy the
problem?? I'm running on a Linux box.
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Loading required package: Matrix
Loading required package: lattice
Error in dyn.load(file, DLLpath = DLLpath, ...) : 
? function 'cholmod_l_start' not provided by package 'Matrix'
Error: package/namespace load failed for ?lme4?
Error: package/namespace load failed for ?lme4?