Same here, I've got one machine already mining but the other which was stopped (so my daughter can play the Sims) can't start mining now but works with other pools.
CGMiner can't find work, GUIMiner says no JSON object could be decoded yet the other machine which has been running all day continues to mine.
I'm having similar problems one machine, Laptop, which gets stopped and restarted often can't connect to slush today, but can other pools.
Other two miners on different machines are humming along no problem.
Even tried to create a new worker and it won't json authorize or somesuch language...
I got my machine using GUIMiner to log in by changing the settings. Instead of using the preset url settings for Slush's Pool(which is
) I changed it 'other' and gave it the host name 'stratum.bitcoin.cz' and port 3333, then it found work and started as soon as I ran it.