Try un-installing the World of Minecraft client COMPLETELY and re-downloading it. Make sure you have the latest version which can be acquired by clicking here.

Make sure you are using your Minecraft.net log-in details and not your womjr.com/worldofminecraft.com details. 

If re-installing the client doesn't work, try signing into another Minecraft account through it.

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Another thing you could try is running  your computer/laptop through a different internet connection. If you are at a friends house, perhaps, ask to use their WiFi. Because, obviously you have to be connected to the internet to get on World of Minecraft, and, if you are not correctly connected you will get the authentication error. 

If all else fails, run the World of Minecraft client on another computer account, or, if possible, another computer all together.

Hope I helped!