Again, waking up an old thread:
I first used an air compressor, set around 50psi, to "air out" all the ports.
Then I used a clean cloth to dab a bit of alcohol on an SD card's contacts... slid it in and out several times, dabbing a little more alchol each time... and voila!
All of our SD cards now seem to work fine... recognize, read, eject...
Also used alcohol to clean the contacts on all the cards.