ERROR: Cookies are blocked or not supported by your browser. You must enable coo

Hello,
I contact you regarding a cookie issue I have. When i try to login i have the following message : “ERROR: Cookies are blocked or not supported by your browser. You must enable cookies to use WordPress.” When I try to the second time. it works….I use Musexpress 2.0 and they said that the issue comes from your plugin. Can you assist me. Many thanks.