cannot upload my prezi to prezi.com / cannot "Sync with Prezi.com"

Please help.

I cannot upload my prezi to prezi.com. I get an "upload failure" message underneath the presentation image when I choose "Sync with Prezi.com."

I am using version 5.0.5 for windows. The presentation shows as "Only on computer." I've searched prezi.com, and it's not there, so it's not syncing automatically.

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