Not able to loggin into yahoo messanger

I was logged into yahoo messanger suddunly i got message that”you have been signed off because you
signed in on a different computer or device.”
This had happened yesterday but after 5 minutes it allowed me to loggedin. But today i am anot able to loggin into Messanger. Other users also getting same message on their PC. In our company
Pl. let me know if i need to do any changes on my PC or on the server. (Proxy settings)

Thanks a Ton for ur help in adnace.