Looks like
blockchain.info is undergoing maintenance currently. Perhaps that is why blocks are showing up invalid? If Slush is using blockchain.info for verification (as it appears he might be), then this could be causing our invalid block issues.
actually, the first 2 were invalid at a time when blockchain.info was still up.
I wonder what mechanism they are using to pull the data from blockchain.info. If only part of the site was down, say the mechanism that feeds out block information, then it is possible this could have caused an error on the pool. Could also just be Slush's pool having some issues as well. I am very glad this is now fixed though.