Lightroom 4: error while Reading Preview Cache

Neither LR4.2 or LR4.3rc succesfully opens; both versions exit the init process and a comment window deploys that declares program has to close because "Lightroom encountered an error when reading from its preview cache and needs to quit. Lightroom will attempt to fix this problem the next time it launches." It never does recover. Using Windows-7, sp1.
2 people have
this problem