I'm trying to upload a game but it won't let me.
it always says, "Error: serialization, buffer too small for compressed data."
What is wrong? and how can I fix it?
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Hmmmm... That's weird! Check that your project isn't above 10MBs in size. If it isn't, then try uploading a blank project

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Whenever you upload something to Scratch, by default, the project is compressed. That error sometimes up when you can't compress any further.
This problem is listed as #8 on the list of Problems that have been resolved already (speaking of which, the next time you encounter an error, check this thread first as it contains the solutions to the most common problems on Scratch ;D). Here's the given solution:
If you try and upload a project with specific graphics, you can receive this message: Failed: Serialization: buffer too small for compressed data.
To fix it, uncheck the small box that asks if you want to compress your sounds and images.

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So now you say in a report that you are getting the Failed Unknown Error message. I've heard that that often relates to a slow internet connection. Maybe try loading again a few times? If you have a laptop, maybe you could try loading from a different internet connection point, like a library and see if that makes a difference.
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