Comment on Stallion WordPress SEO Theme by SEO Dave.

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WordPress Error Message – Are you sure you want to do this? Please try again

And you’ll see there’s a lot of causes of this error, had one other customer with this issue:

Looks like it was a max upload file size issue (many hosts have max upload size at around 2MB, Stallion needs around 10MB) which would normally give a different error. Might be another cause for you, for a quick fix try installing using FTP.