Obviously, you mean this publication: https://www.researchgate.net/publication/231683017. It is very strange that this "co-author", who is not a person, has a personal ResearchGate account: https://www.researchgate.net/profile/Gsar-Publisher
See "A researcher has wrongly claimed co-authorship of my publication" in https://explore.researchgate.net/display/support/Authorship for instructions how to correct this. But unlike this help page suggests, most probably it was not the other "author" himself who wrongly claimed authorship, but ResearchGate's automatic algorithm wrongly identified this account as co- author and assigned your publication also to his profile. This is a frequent problem in ResearchGate, but usually with real persons.