Hmm, I've never heard of that error before.
Errors with Scratch projects sometimes occur due to version conflicts (an old version of Scratch will not be able to open Scratch projects designed in newer versions). Perhaps you may need to download and install the newest version of Scratch (version 1.4) if you haven't done so already.

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1) Are you talking about installing scratch itself, or downloading a project?
2) Does the error show up in scratch, or your browser?
3) Which project (if it is one) are you trying to download?
4) Which version (if you are downloading scratch) of scratch is giving you grief?
5) Which version of scratch do you already have?
6) What OS and SP are you using?
With this information, I can probably fix your problem.
Without it, I really have no idea what the problem even is.
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