Please deregister your license key from website, then get into that api tool I sent you before and check, if the license key is not registered anywhere.
Then, please disable all of the plugins, register the license key and try to update the Layer Slider like 3-4 times.
Comments
this message could mean that your license key is used on more than one domain.
Please use this tool to manage your license keys:
http://forum.muffingroup.com/betheme/discussion/36219/cannot-register-deregister-your-license-key-use-this-tool#latest
thanks