[Help Wordpress]uploading to wordpress plugin directory

I have tried numerous times to upload royalslider to my plugin directory without success.
Already read the knowledgebase articles but still can't install it.
This is the message I get in wordpress
"Unpacking the package…

Installing the plugin…

The package could not be installed. No valid plugins were found.

Plugin install failed."
Any ideas?

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help.dimsemenov.com