Just installed popup plugin but seems there is an invalid argument

Hi,
I just added the wpmudev's Pop Up plugin and straight away got a warning appearing on the home page of the site - see here - https://monosnap.com/file/47cgzUJpRsG84pKeY7qoyYH0Fhwzm2

https://monosnap.com/file/2zNOmILqRZq2qaWb2Y0ofCEyIWFLEQ

Domain: http://tinyurl.com/os5qcku
Support access is ACTIVE until August 28, 2015 12:42 pm

Thanks
Tom